Aleksandar Kovacevic booked his place in the Hamburg Open quarter-finals after coming from a set down to stun Felix Auger-Aliassime on Wednesday. 

Lucky loser Kovacevic earned an impressive 4-6 7-5 6-4 win in two hours and 22 minutes to stun the top seed, though he was up against it after losing the opening set. 

Auger-Aliassime took the early lead at the third time of asking, only for his American opponent to reel off four of the last five games in the second set to take the match the distance. 

Kovacevic looked to have missed his opportunity of causing an upset when he found himself 3-0 down in the decider, but he won the final five games to seal his spot in the last eight. 

"When you get a second chance like this, there is a bit of a feeling of, 'There is nothing to lose out here'," Kovacevic said. "You're maybe a tad more relaxed.

"I'm a bit of a pessimist in life, so for me to come back as a lucky loser, I was not super excited about it.

"Everyone was telling me, 'You have to be grateful for your second chance. You have to use it'. It seems like I might be using it this week."

There was also an early exit for fifth seed Karen Khachanov, after losing to Ugo Humbert as the Frenchman came through his second consecutive deciding-set tie-break.

Humbert emerged a 6-3 3-6 7-6 (7-3) victor to advance to his third quarter-final of the season, while Tommy Paul edged a three-set thriller with Tomas Etcheverry to progress.

In an engrossing three-and-a-half-hour tussle, Paul had to save seven match points against his Argentine opponent to seal a remarkable 6-7 (5-7) 7-6 (7-5) 7-6 (9-7) triumph.

There was no such trouble for third seed Alex De Minaur, though he also needed three sets to confirm a 6-2 4-6 6-4 victory over Spain's Alejandro Davidovich Fokina. 

At the Geneva Open, another top seed was toppled in Taylor Fritz, who saw his return from injury ruined by Alexei Popyrin, as he came out on top with a 6-4 6-4 victory. 

Three-time champion Casper Ruud also continued his good form on clay with a comfortable 7-6 (7-2) 6-2 win against Raphael Collignon, while Learner Tien also advanced. 

Tien needed two tiebreaks to beat Stefanos Tsitsipas 7-6 (7-4) 7-6 (7-2), while two-time winner and home favourite Stan Wawrinka lost in straight sets to Alex Michelsen. 

Data Debrief: Kovacevic joins Sampras and Agassi in Hamburg history books

Kovacevic lost to Arthur Gea in the final round of qualifying in Hamburg, but received a lucky loser spot and then defeated the Frenchman in the opening round of the main draw.

Two weeks earlier in Rome, he also entered as a lucky loser, but he is making the most of his opportunity here. 

And in reaching the quarter-finals, Kovacevic became the first American quarter-finalist in Hamburg since the great Andre Agassi and Pete Sampras back in 1995.