Borna Coric ended Roger Federer's 20-match winning streak on grass, beating him 7-6(6), 3-6, 6-2 in the Halle Open final on Sunday while also bringing to a halt the Swiss maestro's reign as World No 1.
Federer was denied a 10th title in the German grasscourt tournament as Croatian Coric handed the 36-year-old his first setback on an otherwise serene road towards defending his Wimbledon title.
The defeat meant that Rafa Nadal will return to the top of the world rankings on Monday.
Coric, playing in his first grasscourt final, showed great mental toughness and determination to fend off two set points before clinching the opening set after 57 minutes.
Federer responded by applying further pressure on Coric's serve in the second set before converting a break point in the eighth game to force a decider.
The 21-year-old then broke Federer in the sixth game of the final set when the Swiss sliced a backhand long, before claiming only his second ATP title.
Cilic battles past Djokovic to claim Queen's title
Top seed Marin Cilic saved a match point before edging past Novak Djokovic 5-7, 7-6(4), 6-3 to win his second Queen's Club Championships crown on Sunday.
Cilic, who last won the title in 2012, controlled the early exchanges from the baseline but missed six break point chances in the opening set, allowing Djokovic to battle back.
The 31-year-old Serb took his chances with a couple of crisp forehands in the 12th game to break the Cilic serve and claim the first set after an hour long battle.
A rampant Djokovic conceded just one point on his first serve during the second set and looked favourite to close out the contest in the ninth game but Cilic responded with a booming serve out wide to save match point.
A rare double fault from Djokovic at 4-4 in the tiebreak gave Cilic a way back into the match and the Croat took charge by winning the next three points to force a decider.
With momentum back on his side, Cilic looked comfortable in the west London sunshine as he grabbed the only break in the final set to claim his first title of the year.
Kvitova sees off Rybarikova to retain Birmingham title
Petra Kvitova displayed her credentials for a third Wimbledon title after beating Slovakia's Magdalena Rybarikova 4-6, 6-1, 6-2 to defend her title at the Nature Valley Classic in Birmingham on Sunday.
The 28-year-old Czech claimed her fifth WTA title of the season, as well as a tour-leading 37th match win of the year, as she came from a set down to triumph.
Rybarikova started the contest on the front foot, punishing Kvitova for her whopping 22 unforced errors by converting two break points to take the opening set.
Kvitova, on the back of fine serving, then roared back with consecutive breaks before levelling the match and then moved up another gear to dominate the final set with a string of powerful forehand winners.
"It's amazing to defend a title," Kvitova said courtside. "It's not happened in a long time for me.
"I was too nervous and Magda put pressure on me in the first set. It was tough to fightback but I was relaxed and it paid off afterwards.
"I'm going to Eastbourne (this week) for another tournament. We'll see how it goes from there... but for sure Wimbledon is the next big one for us."
Kvitova will be joined by the top two players in the world - Simona Halep and Caroline Wozniacki - and defending champion Karolina Pliskova in Eastbourne, the final tune-up event ahead of Wimbledon, which begins on July 2.