Even Carlos Alcaraz's energy levels were running low as he found himself in a battle with American Tommy Paul on Thursday but the glint of an Olympic medal for Spain helped refuel his engine.
The 21-year-old prevailed 6-3, 7-6(7) to reach the semi-finals on his Games debut, but in cloying humidity he had trailed in the second set, looking flat and frustrated.
It was hardly surprising, his seventh match in six days coming came the day after an emotional doubles defeat with his idol Rafa Nadal in what could have been the latter's last Roland Garros match.
Second seed Alcaraz was kicking the hoardings in frustration at one point as he trailed 5-3 with Paul bossing the match.
He snapped out of his slump, however, and is now two wins away from adding the Olympic gold to a spectacular year which has brought him the French Open and Wimbledon titles.
"I was trying to raise the adrenaline and the intensity and the truth is that it helps to know that you playing for Spain, we are playing and representing our flag," Alcaraz told reporters.
"That helps a little more to leave everything on the court, to continue fighting, to keep running and not give up."
Alcaraz hit the ice bath after beating Paul and will need a quick recovery for his semi-final against Canada's Felix Auger-Aliassime, who beat Norwegian clay-court specialist Casper Ruud 6-4, 6-7(8), 6-3.
"Singles, doubles, not a day of rest in between, but the Olympics are every four years and you have to accept that," the four-times Grand Slam champion said.
"You have to accept it, you have to fight an try to do everything perfect off the court."
Even when not playing at his highest level, Alcaraz's presence on court can make the difference.
Ninth seed Paul will look back at pivotal moments, not least the set point he had in the second set tiebreak when he did not do enough with a half volley and Alcaraz sprinted across court to punch a backhand down the line.
"It was a honestly a difficult moment in the second set but representing Spain helps a lot to increase the level," he said.
"Tommy played great tennis but I'm happy I found solutions."
China's Zheng shocks Swiatek in semi-finals
World number one Iga Swiatek said she "messed up" and could not hold back the tears after a shock loss to China's Zheng Qinwen in the Olympic semi-finals at Roland Garros on Thursday.
The Pole, who was on a 25-match winning streak at Roland Garros, was a clear favourite to win the gold medal after a third consecutive French Open title this year.
"I had a hole in my backhand," she told Eurosport Poland. "It happens rarely because it is usually my most solid stroke."
Swiatek held a 6-0 career record against Zheng, but the 23-year-old claycourt specialist produced one of her worst displays of the season, making 36 unforced errors against her opponent's 15.
The five-time Grand Slam champion blamed stress and a lack of time between matches for her performance.
"I was not technically well positioned because of the stress and the fact that I played my games day by day. We didn’t have time to adjust that and work on that," Swiatek said.
"I know that’s not the justification but I tried to correct that during the match. Today it didn’t work at all. So she used that to win the game," she said.
Swiatek refused to take questions from international reporters after the match. "Sorry, next time," she said.
It has been a tough week for Swiatek who was hit by a ball in her quarter-final win over Danielle Collins on Wednesday.
Collins accused the Pole of being "insincere" after the American abandoned the match due to stomach pain.
Collins blamed her injury on the lack of fresh water on the courts, which she said provoked heat stress and convulsions, amid extremely hot weather.
The Pole still has a chance to win a medal and will play the loser of the other semi-final between Croatian Donna Vekic and Slovak Anna Karolina Schmiedlova.
Zverev beaten, Djokovic through
Novak Djokovic's hopes are intact despite a scare.
There will be a first-time Olympic men's singles champion after Tokyo winner Alexander Zverev crashed to a quarter-final defeat against Italy's Lorenzo Musetti.
Men's top seed Djokovic was imperious as he won the first set against Tsitsipas. But he went a break down in the second and more worryingly appeared to have aggravated the knee that required surgery after the French Open.
He needed treatment at a change of ends and almost went 5-1 down before recovering and surging back to seal victory.
Djokovic will now aim to snap his semi-final curse and beat Musetti, a 7-5, 7-5 winner against Zverev.
"I didn't feel good the whole week. And the second round, I felt horrible on the court. I felt horrible today by the end of the first set," third seed Zverev said. "It's upsetting."
United States duo Rajeev Ram and Austin Krajicek followed up their defeat of Spain's Alcaraz and Rafa Nadal the previous evening to book their place in the final as they overcame Czech pairing Tomas Machac and Adam Pavlasek 6-2, 6-2.
