(CNN) Andy Murray began slowly in his first match as the new men's No. 1 in tennis but finished in style, defeating Marin Cilic at the World Tour Finals on Monday.
The Scot joined Kei Nishikori atop the John McEnroe group with a 6-3 6-2 victory -- his 20th win in a row -- to avenge a defeat to the Croatian in August at the Cincinnati Masters.
How Murray must have reveled in being introduced as the world No. 1 ahead of the clash in London, not far from his residence, after overtaking Novak Djokovic as No. 1 a week ago. He received a rousing reception and is clearly the crowd favorite at the event, given Roger Federer's absence.
But Murray hardly has time to sit back and enjoy his immense accomplishment, since the Serb is almost assured of regaining top spot if he wins the tournament -- and despite a recent slump, he is the four-time defending champion.
Eight of the best
Murray has the highest win percentage on the tour this year and, having followed in the footsteps of Tim Henman (2003) and Greg Rudedski (1998) with victory at the Paris Masters earlier in November, he's now attempting to become the first Brit in history to win the ATP World Tour Finals. A "Group of Death" stands in his way -- with world No.3 Stan Wawrinka having won seven of his 16 matches against Murray in his career. But, in the midst of a 19-match winning streak, Murray won't want to concede the world No.1 spot any time soon.
• Titles in 2016: 8 - Wimbledon, Olympics, Queen's Club, Paris Masters, Rome Masters, China Open, Shanghai Masters, Vienna Open
• Aces in 2016: 527
• Win percentage in 2016: 89% -- highest of the eight contenders
Facing world No.1s in major finals, Wawrinka has never lost -- beating Rafa Nadal in Melbourne (2014), Djokovic at Roland Garros (2015) and the Serb once again at this year's US Open. A man for the big occasion, Wawrinka holds a 100% record against Djokovic in grand slam deciders, but has never otherwise beaten him (0-19). With the US Open title to his name, Wawrinka became the oldest Grand Slam champion (31) since Andre Agassi at the 2003 Australian Open. A remarkable run of winning 11 straight finals only came to an end when he suffered a shock loss in St Petersburg to Alexander Zverev -- citing him as the
"future of tennis." • Titles in 2016:
4 - US Open, Geneva Open, Dubai Championships, Chennai Open
• Aces in 2016:
436• Win percentage in 2016:
74%
The highest-ranked Asian player in ATP history, Kei Nishikori captured a fourth straight title at the Memphis Open in February before going on to win Olympic singles bronze in Rio, beating Nadal in three sets. Nishikori, 26, is the first Japanese singles medalist since Ichiya Kumagae at Antwerp 1920.
• Titles in 2016: 1 - Memphis Open
• Aces in 2016: 245
• Win percentage in 2016: 76%
Standing at 198cm, Cilic is the tallest of the ATP finalists and a full 20cm taller than opponent Nishikori. He reached a third consecutive Wimbledon quarterfinal in 2016, but lost out to Roger Federer despite leading by two sets and holding three match points. Capping a resurgent end to 2016, Cilic has led Croatia to the Davis Cup final with wins over Belgium, USA and France, and will take to the court against Del Potro's Argentina later in November. Murray partly has Cilic to thank for his No. 1 berth -- he upset Djokovic with a supreme display of power tennis in the Paris Masters quarterfinal, beating the Serbian for the first time in his 15th attempt.
• Titles in 2016: 2 Cincinnati Masters, Swiss Indoors Basel
• Aces in 2016: 636
• Win percentage in 2016: 69%
Djokovic became just the third man in history to hold all four majors at once when he won the French Open in June, and the first player to surpass $100 million in prize money. For now, his throne has been seized by Murray, but it would surely be unwise to write him off; Djokovic is bidding to capture his fifth successive ATP World Finals title, and would move ahead of Pete Sampras and Ivan Lendl in the overall list of winners, equaling Federer with a sixth title. The Serb has never lost to any of his opponents in the Ivan Lendl group -- Gael Monfils (13-0), Dominic Thiem (3-0) and Milos Raonic (7-0) -- and still retains a 71% career win percentage against Murray.
• Titles in 2016: 7 - Roland Garros, Australian Open, Canada Masters, Miami Masters, Madrid Masters, Indian Wells, Qatar Open
• Aces in 2016: 264
• Win percentage in 2016: 88%
Already the first Canadian man to break into the ATP top 10, Raonic became the first to reach a major singles final when he met Murray at Wimbledon. That coveted first Grand Slam title may have evaded him, but he did take the Brisbane International at the turn of the year. Raonic nailed a slam dunk at the 2016 NBA All-Star Celebrity Game, helping Canada beat USA 74-64. And his 6-feet 4-inch stature also helps him on the tennis court ... He wins 90.6% of service games -- the third highest percentage on the tour in the past year (after Ivo Karlovic and John Isner) -- and has the fastest serve (career-best 155.3 miles per hour) of all the ATP World Tour finalists. The Canadian, 25, has also saved an impressive 70.2% of break points -- the highest proportion of the eight.
• Titles in 2016: 1 - Brisbane International
• Win percentage in 2016: 77%
• Aces in 2016: 824
For so long looked upon as an entertainer rather than a genuine threat, Monfils is making his ATP World Tour Finals debut in 2016, having produced a career-best season in his 30th year. He reached his first Grand Slam semifinal for eight years at Flushing Meadow, and though he may have eventually lost out to Djokovic, he boasts a higher break point conversion percentage than any other player at the finals. It's been a promising year for the Frenchman; consistency allied with his undeniable talent could see Monfils finally hit the heights he's hinted at.
• Titles in 2016: 1 - Washington Citi Open
• Aces in 2016: 471
• Win percentage in 2016: 75%
The last man to qualify for this year's event, Thiem is the youngest player at the finals and the first Austrian to take part in the singles since former world No.1 Thomas Muster in 1997. He may have lost out to Djokovic at Roland Garros -- his first ever grand slam semifinal -- but boasts a 90.9% win percentage in deciding sets in 2016 -- the highest proportion of any player on the tour to have started 25 matches or more. Not bad at all for a 23-year-old.
• Aces in 2016: 462
• Win percentage in 2016: 72%
• Titles in 2016: 4 - Stuttgart's Mercedes Cup, Open de Nice Cote d'Azur, Acapulco's Abierto Mexicano Telcel, Argentina Open
Perhaps the pressure of playing his first match when atop the rankings against a grand slam champion -- this was no easy first-rounder at a major -- plus fatigue accounted for Murray's noteworthy demeanor in the early going.
He appeared to complain to the chair umpire Damian Steiner about noise from the crowd during points, jawed at his support camp -- that, however, is nothing new -- and took over the allotted limit of time between points. In the seventh game he looked utterly spent.
Or perhaps not.
"I didn't feel any more nervous than usual," said Murray. "It's just quite different conditions in there than what we've been practicing in during the week. It's a lot slower than it has been."
After the 6-foot-6 Cilic missed his opportunities in the tense opener, often undone by his shaky forehand, Murray found things much simpler in the second set.
Murray went 4-for-5 on break points compared to Cilic's 1-for-5. Cilic's bright yellow shorts turned out to be louder than his game.
"When you start winning, you gain confidence," Murray told the crowd in an on-court interview. "In the important moments today, on the break points, I was a little more solid than Marin.
"He had some chances in the first set and the beginning of the second set. When I had my opportunities I took them. That's what winning matches does for you.
"It was a great atmosphere.
"I'll try and keep going until the end of the year now."
His next challenge comes from Nishikori, one of only two players to beat Murray since the start of September. It was the Japanese baseliner who upset the three-time grand slam winner in five sets in New York.
Read: Murray ousted in New York
Cilic claimed his first Masters title by downing Murray in Ohio and carved out two break points Monday in the first game. A good second serve from Murray saved one, while an errant Cilic forehand accounted for the other.
Three breaks of serve ensued, with Murray saving a break point at 3-1 with an ace.
Cilic gathered momentum on his serve from late in the first set to 2-1 in the second -- Murray had fended off another break point at 0-1 with an ace -- yet didn't win another game.
It led Murray, who has never made the final at the tournament, to proclaim: "It's one of the best matches that I've played here over the years."
Earlier Monday, Nishikori toppled another three-time grand slam winner, Stan Wawrinka, 6-2 6-3.
Djokovic seeks to improve to 2-0 in the Ivan Lendl group -- Lendl is one of Murray's coaches and has been influential -- when he plays Wimbledon finalist Milos Raonic on Tuesday.