Carlos Alcaraz overcame illness to defeat Andrey Rublev at the ATP Finals in Turin.
The 21-year-old Spaniard won 6-3 7-6 (10-8) despite cutting short his practice session on Tuesday after struggling with a chest complaint.
German second seed Alexander Zverev later claimed his second victory with a 7-6 (7-3) 6-3 win over Casper Ruud in the John Newcombe Group.
Zverev will guarantee his place in the semi-finals if he beats Alcaraz in the final round of the group stage on Friday.
Sporting a pink nasal strip to help his breathing, third seed Alcaraz won four consecutive games against Rublev to take the first set in 37 minutes with a double break of serve.
He claimed the second in an epic tie-break, hitting 33 winners overall in the match compared to 14 for the Russian.
“I surprised myself the way I played from the baseline. I was really calm,” Alcaraz said.
“I just focused on my game and what I have to do and forgetting I’m not feeling well.”
Alcaraz scribbled ‘Valencia’ on a TV monitor after his victory to show support for compatriots hit by recent floods.
The French Open and Wimbledon champion was out of sorts when losing his first match in Turin on Monday to Norwegian Casper Ruud.
And while he used a chest rub during breaks in play on Wednesday, his movement was much sharper.
He came from 40-15 down to break for a 4-3 lead in the opening set after Rublev fluffed a straightforward forehand at deuce.
And the Russian squandered a 30-0 advantage on his next service game as his opponent secured the set.
Eighth seed Rublev, who lost his opening match to German Alexander Zverev, held serve to force a tie-break in the second.
An early break gave Alcaraz the edge, although he was pegged back and had to save two set points before clinching victory.
Rublev has now lost six successive matches at the ATP Finals in straight sets since reaching the semi-finals in 2022.
Two-time champion Zverev wins again
Zverev, seeking his third ATP Finals title, followed up his defeat of Rublev with a straight-set win against Norwegian sixth seed Ruud.
Ruud only missed six of his first serves in the first set but Zverev dominated the tie-break after the opening 12 games yielded no break points.
With an hour and 20 minutes gone, Zverev finally secured a break to go 5-3 up in the second set and served out to love for victory.
“I think it was a very good match actually from both of us,” he said. “I’m happy to win today but it was very, very close.”
On Thursday, American Taylor Fritz faces Australian Alex de Minuar (13:00 GMT) in the final round of Ilie Nastase Group matches.
World number one Jannik Sinner will reach the last four if he claims a set against Daniil Medvedev (19:30), and will top the group with a third straight win.
