Roger Federer joins Novak Djokovic in the third round of the Shanghai Masters after winning by the skin of his teeth, while Rafael Nadal crashed on a day of shocks.
World No.3 Federer will unseat second-placed Nadal in the ATP rankings on the back of his incredible victory.
The Swiss player saved five match points, including three at a third set tie-break, before converting his first chance to seal a gripping 7-5 3-6 7-6 (9/7) victory against Leonardo Mayer.
The 17-times grand slam winner needed to draw on all his years of experience to remain level-headed as he closed out the game, leaving his Argentine opponent distraught as he trudged off the court.
Second seed Nadal, meanwhile, battled the early stages of appendicitis and a ruthless Feliciano Lopez in his 6-3 7-6 (8/6) opening game loss.
The current world No.2 was diagnosed with appendicitis on Sunday but did not show any obvious signs of suffering from it in the match.
But he was still far from his world-beating best as he returns to competition following three months on the sidelines.
Elsewhere, Serbian world number one Djokovic claimed a 6-3 6-4 victory against Austrian Dominic Thiem, the youngest player in the top 50.
But it was agony for Australian Open champion Stan Wawrinka, who crashed out of his second successive tournament at the first stage – despite leading his final set 3-0.
The fourth seed was in need of a morale-boosting victory after his last outing resulted in a first round exit at the Japan Open to 103-ranked Tatsuma Ito.
The world No.4 started brightly in Shanghai, taking the first set in his tightly-fought battle with Gilles Simon of France.
But his 29th-ranked opponent fought back to earn a 5-7 7-5, 6-4 victory.
The results in Tokyo and Shanghai could undermine Wawrinka’s bid to book his place at the end of season ATP World Tour Finals, which features the world’s top eight players.
“Two first rounds. It’s never easy, for sure,” Wawrinka said.
“I need to accept, go back home, try to focus on the rest of the year because there are so many to play, so many big challenges for me, that I want to be fresh and ready mentally for that.”
The fifth seed in Shanghai, David Ferrer, also faced a tough battle in his opening match, but finally overcame Slovak Martin Klizan 4-6 7-6 (7/4) 6-4.
Ferrer will play Andy Murray in the next round, after the British 11th seed won his match against Poland’s Jerzy Janowicz 7-5 6-2.
Meanwhile, seventh seed Kei Nishikori and 10th seed Grigor Dimitrov both crashed out in their opening matches, beaten by American Jack Sock, and France’s Julien Benneteau respectively.
Eighth seed Canadian Milos Raonic also failed to make the next round, after he withdrew from his match with Juan Monaco of Argentina suffering from fever as he was trailing 5-2.
