LONDON: Argentina's Juan Martin del Potro returned to see off Frenchman Gilles Simon on Tuesday and reach the Wimbledon quarter-finals for the second time, but it was desperately hard work.
The fifth seed had led by two sets on Monday but Simon grabbed the third set before fading light ended play.
With world number one Rafael Nadal waiting for the winner, Tuesday's fourth set, played in much cooler conditions than the first three the day before, turned into a mini-epic before Del Potro eventually prevailed 7-6(1), 7-6(5), 5-7, 7-6(5).
Del Potro looked flat as he was broken to trail 3-1 but he clawed his way back to lead 5-4 with his serve to come.
He looked on the brink of victory when he moved 40-15 ahead but both match points vanished, the second with a double-fault.
Simon failed to convert a break point, then a third match point for Del Potro ended with him netting a forehand.
The 33-year-old Simon saved a fourth match point when he threw the kitchen sink at a forehand return and the world number 53 eventually took his fourth break point to level at 5-5.
The next two games went with serve and the match was well into its fifth hour when the tiebreak began.
Del Potro trailed 1-3 but at 5-5 he fired down a swinging ace to reach match point number five and this time Simon cracked, netting a backhand to the relief of the Argetine who roared his approval.
Serena enters semis
Meanwhile, Serena Williams stayed on track for an eighth Wimbledon title as she fought back to beat Italian Camila Giorgi 3-6, 6-3, 6-4 in a fiercely contested quarter-final on Tuesday.
For the first time in the tournament the 36-year-old was seriously challenged as unseeded Giorgi fought fire with fire to claim the first set on Centre Court.
Williams responded by raising the intensity level and began striking the ball with ferocious power to break Giorgi's serve for the first time on her way to levelling the match.
World number 52 Giorgi dropped serve to love early in the decider but hung in gamely to at least make Williams serve to reach her 35th Grand Slam semi-final and 11th at Wimbledon.
Williams stepped up to the line at 5-4 and brought up match point with an ace before completing victory when Giorgi could only push a forehand into the net.
German 11th seed Angelique Kerber reached the Wimbledon semi-finals with a 6-3, 7-5 win over Russian Daria Kasatkina on Tuesday but needed seven match points to see off the 14th seed.
Twice Grand Slam winner Kerber, 30, will next face Latvian 12th seed Jelena Ostapenko in the last four on Thursday.
The highest seed left in the women's draw, 2016 finalist Kerber was 3-0 up in the first set before her 21-year-old opponent had time to react.
Kasatkina steadied herself to reach 3-4 before she double-faulted on break point and lamely surrendered the game to Kerber, who then served for the set.
That was to be the story of the match with the Russian delighting the gasping crowd with some outrageously talented returns and passing shots only to self-destruct on serve.
Kerber again broke to go 3-1 up in the second set before Kasatkina levelled for 3-3 only for another double fault to put Kerber back in the driving seat.
The Russian broke back again for 4-4 but the German replied in kind immediately.
With Kerber serving for a place in the last four, Kasatkina earned two break points with a forehand and levelled the scores before again failing to hold her serve and being left on the backfoot.
Kasatkina then saved five match points before surviving yet another thanks to Hawkeye, with Kerber's lob landing just beyond the baseline. The German finally won through to the semis when Kasatkina's return found the net.