(CNN) US Open champion Stan Wawrinka suffered a shock defeat to Alexander Zverev in the St. Petersburg final Sunday and then predicted a bright future for the German teenager.
"You are the future of tennis, but you are already at the top," the Swiss star said after losing a three-set battle in the title match at the ATP 250 event.
It was the first title for 19-year-old Zverev, who ended Wawrinka's remarkable run of winning 11 straight finals, the latest his stunning victory over Novak Djokovic in the last grand slam of the season.
The world No. 3 had leveled at one set all and when he moved a break ahead in the deciding set it he looked set for his fifth title this year.
But back came the two-meter-tall Zverev to break Wawrinka's service twice to run out at a 6-2 3-6 7-5 winner in two hours 23 minutes.
"I'm full of emotions! I just couldn't have chosen a better place to win my maiden title," said Zverev, whose Russian father was a professional tennis player.
He is the first teenage winner on the ATP Tour since 19-year-old Marin Cilic at New Haven in 2008.
"Today you've played a great match and won deservedly. My congratulations for what you're doing so far," Wawrinka, 31, added in comments reported by AFP.
Zverev has also had wins this year over top-10 players Roger Federer, in the semifinal of the grass-court event at Halle, and Tomas Berdych this week in St. Petersburg.
Another rising star, 22-year-old Lucas Pouille of France, won the ATP tournament in Metz Sunday with a 7-6 6-2 victory over Austrian top seed Dominic Thiem.
Pouille, who has reached the last eight at Wimbledon and the US Open this year, beating Rafael Nadal at the latter grand slam, was 4-0 down in the first set tiebreak, but battled back to take it 7-5 and then dominated the second set to claim his maiden crown.
On the WTA Tour, former world No. 1 Caroline Wozniacki won her first title of this season.
The Dane repeated her 2010 success by winning the Pan Pacific tournament in Tokyo, beating home hope Naomi Osaka 7-5 6-3, battling an injury scare and a determined young opponent playing her first WTA title match.
"She's going to be a great player, already rising in the rankings so fast. I've no doubt we'll see her in many, many more finals," Wozniacki told the official WTA website after taking her 24th career title.