Washington - World No 6 Stefanos Tsitsipas struggled late but advanced to the ATP Washington Open quarter-finals on Thursday by defeating Australia's Jordan Thompson 6-3, 7-6 (7/4).
The 20-year-old Greek top seed took the only break of the match to claim the first set and after some tense moments won the tie-breaker when Thompson netted a forehand after 99 minutes at the US Open hardcourt tune-up event.
"It was kind of tricky at the end," Tsitsipas said.
"I kept doing silly mistakes in the tie-breaker. I was not happy about it. I made a lot of unforced errors.
"I played great to get break points, then I started thinking about it. I didn't identify the right occasion to come to the net. Just a little lost."
"I believe I can handle those situations more mature in my next matches."
In the quarter-finals, Tsitsipas will meet French 10th seed Benoit Paire, who ousted US fifth seed John Isner 7-6 (7/3), 6-3.
"He's a very dangerous player," said Tsitsipas of Paire.
"He has a big backhand. His serve can be dangerous. I'll have to be careful. He's very unpredictable."
Tsitsipas, who beat Roger Federer in January on his way to the Australian Open semi-finals, seeks his fourth career ATP title after crowns last October in Stockholm, last February at Marseille and in May at Estoril.
Tsitsipas reached the 2018 Washington semi-finals and a week later became the youngest player to ever beat four top-10 ATP players in the same week before losing to Rafael Nadal in the Canada Masters final.
Croatian sixth seed Marin Cilic, the 2014 US Open champion, beat Canadian ninth seed Felix Auger-Aliassime 6-3, 6-4.
World number 17 Cilic booked a last-eight date with Russia's 10th-ranked Daniil Medvedev, who eliminated hometown hero Frances Tiafoe 6-2, 7-5.
"He's in great shape. His game is strong. We all know what he's capable of when he's in good shape," Medvedev said of Cilic.
"It's going to show what I'm capable of this season."
Medvedev and Karen Khachanov give Russia two top-10 players for the first time since October 2010.
"I'm playing good," Medvedev said.
"I want to back it up with some more wins."
Tiafoe said he will skip next week's ATP Canada Masters Canada after aggravating a foot injury in the loss.
Two lucky losers reached the last eight, including Slovakia's Norbert Gombos, a last-second replacement for South African fourth seed Kevin Anderson, who withdrew with right knee pain.
The world number 137 will next face Aussie Nick Kyrgios, who fired 15 aces in eliminating Japan's Yoshihito Nishioka 6-2, 7-5.
German 122nd-ranked lucky loser Peter Gojowczyk shocked Canada's Milos Raonic, the 2014 Washington champion, 6-4, 6-4 to reach the quarter-finals.
"Couldn't make it count when it was the most important," Raonic said.
"Just a disappointing performance."
Gojowczyk, who had lost 12 of 14 prior matches entering the week, replaced Aussie Bernard Tomic, who withdrew with a finger injury.
The German has made the most of his opportunity by dispatching Russian Andrey Rublev, Aussie 12th seed Alex De Minaur and 20th-ranked Raonic.
Next up for Gojowczyk is British 13th seed Kyle Edmund, who ousted France's 70th-ranked Jo-Wilfried Tsonga 4-6, 6-3, 6-4.
Tsonga, who fired 18 aces, received a wildcard into next week's event at Montreal.
"I can take some positive things," Tsonga said.
"I still think I can improve many things and that's why every day I come to the court."
Also getting a Montreal spot was Britain's Andy Murray, who will play doubles alongside Spaniard Feliciano Lopez as he tries to make a singles return in two weeks at Cincinnati.
Murray, who feared he might never play again after January right hip surgery, plays alongside brother Jamie in a Washington doubles quarter-final on Friday.
In the joint WTA event, Taiwan's 31st-ranked Hsieh Su-wei became the only seed in the quarter-finals by outlasting Russian qualifier Varvara Gracheva 7-5, 4-6, 7-6 (8/6).
Results from Thursday's matches at the ATP and WTA Washington Open (x denotes seeding):
Kyle Edmund (GBR x13) bt Jo-Wilfried Tsonga (FRA) 4-6, 6-3, 6-4
Marin Cilic (CRO x6) bt Felix Auger-Aliassime (CAN x9) 6-3, 6-4
Peter Gojowczyk (GER) bt Milos Raonic (CAN x8) 6-4, 6-4
Daniil Medvedev (RUS x3) bt Frances Tiafoe (USA x16) 6-2, 7-5
Norbert Gombos (SVK) bt Miomir Kecmanovic (SRB) 1-6, 6-3, 7-6 (7/4)
Stefanos Tsitsipas (GRE x1) bt Jordan Thompson (AUS) 6-3, 7-6 (7/4)
Benoit Paire (FRA x10) bt John Isner (USA x5) 7-6 (7/3), 6-3
Nick Kyrgios (AUS) bt Yoshihito Nishioka (JPN) 6-2, 7-5
Camila Giorgi (ITA) bt Rebecca Peterson (SWE) 3-6, 6-3, 6-4
Catherine McNally (USA) bt Christina McHale (USA) 6-3, 1-6, 6-3
Zarina Diyas (KAZ) bt Lesia Tsurenko (UKR x5) 6-4, 6-4
Hsieh Su-Wei (TPE x4) bt Varvara Gracheva (RUS) 7-5, 4-6, 7-6 (8/6)