Marathon man John Millman is through to the quarter-finals of the ATP Tour’s Delray Beach Open, his win courtesy of another strong showing in a tie-break.

The Australian, who has been winning tough at Delray, beat American Marcus Giron 6-3 7-6 (8-6) to reach the last eight.

Of the two matches he has played in the tournament, Millman needed four tiebreakers to advance.

In the round of 32, the world No.91 eliminated No.8 seed Maxime Cressy 6-7 (7-2) 7-6 (7-2) 7-6 (7-3).

Both Millman and Giron served five aces each on Thursday, but the Queenslander gained the advantage by converting both of his two break points.

He will now meet either No.3 seed Grigor Dimitrov or qualifier Mitchell Krueger, who beat Australian Jordan Thompson in the round of 32, for a place in the semi-finals.

Joining him in the next round is No.2 seed Reilly Opelka, who rode an unbeatable first serve before eliminating Jack Sock in a 6-7 (8-6) 7-6 (7-4) 6-1 victory.

It was Opelka’s sixth consecutive victory at Delray, where he was the 2020 champion.

Opelka had 21 aces, just one double-fault, and won a staggering 53 of 56 points when he landed a first serve. He faced only one break point all day, which he saved.

“I competed really well,” Opelka said.

Opelka will face either seventh-seeded Adrian Mannarino or Brandon Nakashima in the quarters.

Opelka had a pair of unforced errors to end the first set, as Sock won the opening tiebreaker – Opelka’s first loss in his last seven tiebreaks after going 6-0 in those situations on his way to winning a tournament in Dallas two weeks ago.

But he knotted the match by winning a second-set breaker, then ran away in the third set.

“He was starting to fatigue a lot,” Opelka said.

All four quarter-finals are scheduled for Friday.

Top-seeded Cameron Norrie meets Sebastian Korda in a rematch of a 2021 Delray semi-final while No. 4 seed Tommy Paul will play Stefan Kozlov.

Opelka and Millman will play night matches.