Jack Draper overcame a stomach bug and scorching temperatures to defeat close friend Jack Pinnington Jones at the Lexus Eastbourne Open.
In baking conditions on the south coast, Draper booked a place in the quarter-finals of the Wimbledon warm-up event with a 7-5 6-4 victory as he continued his comeback from persistent arm and knee injuries.
Victory in an hour and a half maintained his encouraging start under new coach Andy Murray and will see the former world No 4 will face Canada's Gabriel Diallo on Thursday for a spot in the semi-finals.
In the searing conditions, Draper wore a protective sleeve on his left arm, but insisted it was not fitness-related.
"I've always worn a sleeve for sweat because otherwise I sweat very heavily and the grip gets destroyed very quickly," said Draper, who was playing only his second match in more than two months.
"It wasn't to do with my arm injury. I had a bit of a stomach ache, stomach bug today, so I was struggling a little bit with that.
"But, apart from that, playing these matches again, when you test yourself, when you come through tough sets in tough conditions, it gets easier as it goes along.
"You get more and more conditioned to competing. It's obviously very different to the practice court so every match I'll keep getting better and better on that front."
With weather warnings in place due to extreme heat, temperatures had dropped slightly to 30 degrees Celsius when Draper and Pinnington Jones eventually came on court late on Wednesday afternoon.
Draper, who again had two-time Wimbledon champion Murray offering encouragement from the sidelines, began confidently in his bid to back up Monday's straight-sets success over American Marcos Giron.
The 24-year-old broke his opponent in just game three but later squandered a set point at 5-4 up with a forehand which flew into the stands.
Pinnington Jones duly capitalised to level by taking advantage of his third break point courtesy of a fortunate, net-cord winner.
However, the 23-year-old then failed to hold as Draper regained the initiative before clinching the opening set with successive aces.
Pinnington Jones, who reached round two on his Wimbledon debut last year, again dropped serve at the start of the second set.
The world No 145 recovered to remain in touching distance but, following a brief disagreement with umpire Scott Noble over the time allowed at changeovers, was unable to prevent Draper progressing in an hour and a half.
"Jack's a great friend so it's tough playing against a good friend," said Draper.
"He's still young and he's been building his way up the rankings, he's nearly in the top hundred. He's going to be someone who's going to be a top, top player, and I think he showed that today.
"There were no hard feelings (about the crowd shouting "come on, Jack") as I didn't know who you guys were supporting!"
Murray was cheered by the Devonshire Park crowd when he arrived and offered vocal support throughout.
"When he walked on court, people obviously noticed and a bit of noise for him - I'm not sure if he likes that too much," Draper said of Murray.
"But that's what comes with it. Andy's a legend so everyone loves seeing him."
Draper, who enjoyed a straight-sets success over American Marcos Giron in his comeback match on Monday, continued: "It's really good to have that support from Andy.
"He absolutely loves being back in tennis again. It's his passion, competing and that overall buzz of a tennis environment.
"I think Andy's the ultimate competitor in that way and the more I'm around him, the more I see he's really enjoying being back around tennis, which is really nice for me and also him.
"It's very nice to have him calling me on."
In Wednesday's first all-British showdown on Centre Court, Jan Choinski defeated Wimbledon wildcard Felix Gill 6-4 6-7 (4) 6-2.
Choinski was initially due to face world No 7 and defending champion Taylor Fritz before the American withdrew injured, allowing 24-year-old Gill an opportunity as a lucky loser.
Earlier, British No 5 Toby Samuel registered his first ATP Tour victory by beating Argentina's Thiago Agustin Tirante.
The 23-year-old, who is poised to make his Wimbledon debut next week, won 6-1 7-6 (7) and will take on world No 21 Juan Manuel Cerundolo in the last eight.
However, there was agony for Arthur Fery, who was beaten by Argentinian eighth seed Cerundolo, 6-2 7-6 (2).
Zeynep Sönmez, who knocked out Harriet Dart in the first round, advanced to set up a quarter-final against No 3 seed Jelena Ostapenko after Czech player Sara Bejlek withdrew from their match.
Madison Keys set up an all-US tie with McCartney Kessler as she defeated Jessica Bouzas Maneiro 6-4 6-3 while Kessler bested Australian Kimberley Birrell 6-1 6-4.
American Emma Navarro booked her place in the quarter-finals of the Bad Homburg Open after sealing a sensational 5-7 6-2 3-6 victory over world No 3 Iga Swiatek.
Navarro was held to 1-1 by Swiatek but produced some exceptional tennis in the third set, dropping only three games as she secured victory.
Elina Svitolina was due to face Wang Xinyu in the quarter-finals but was forced to withdraw from the match due to a right hip injury.
"Hi guys, it's Elina here. Unfortunately, I will be pulling out of my quarterfinal match here in Bad Homburg," Svitolina said in a video posted on the tournament's X account. "Last night was a hard-fought victory, but it took a little bit more than expected out of my body, so I need a few more days to recover.
"I wish all the best to all the players who are still competing, and a lot of success to the tournament, and I will hopefully see you all next year."
