Latvian qualifier Gulbis, a former world number 10 also looking for his first quarter-final at Wimbledon, gave as good as he got in a ding-dong battle over three sets before hurting his knee in the third-set tiebreak.

Japanese former world number four Nishikori, seeded 24th, was troubled by his right elbow during the first set which he lost after being broken in the fifth game.

Gulbis, who won the ace count 18-7, beat Nishikori with a chip at the net to give himself two set points and took it on the first.

"My elbow was bothering me... It wasn't working well for me first set," said Nishikori. "He was playing very good, very good serves. I mean, first couple sets I couldn't really do anything with his serve. So I was struggling returning his serve.

"Getting the second set tiebreak gave me a lot of confidence."

The next two sets were a battle of attrition with Gulbis moving his opponent from side to side and hitting crosscourt backhand winners, while Nishikori hung in on the rallies.

Nishikori took the second set after going into a 5-1 lead in the tiebreak. A fine chip gave the Japanese a set point at 6-3 but Gulbis rallied with an ace followed by a neat drop shot, before Nishikori sealed it when the Latvian returned long.

"I think I should have won the second set. I think I should have played more aggressively on my return games," Gulbis said. "I was serving better, but he was going for his shots better than I did.

"He's a fighter... I was unfortunate in the third set, yes, but in the second set he found a way to win it, so this was the key today."

TREATMENT

The third set tiebreak was more dramatic with Gulbis going off for treatment after slipping and hurting his left knee and coming back on with it heavily bandaged.

"I think I have a small tear in this ligament here, so I will check with the doctors. I don't think it's very good. I think I need some recovery for it, maybe two, three weeks," Gulbis said.

"The physio told me that I cannot really make it worse, and he taped it... I just didn't want to pull out so I could even take the third set."

The Latvian saved two set points with some strong returns but both players made unforced errors, Gulbis missing a volley and Nishikori serving two double faults before the Japanese finally clinched it 12-10 after almost three and a half hours.

Gulbis, who had won three five-set matches to get to the fourth round including his upset over fourth seed Alexander Zverev, quickly fell 5-0 behind in the fourth set but managed to hold serve in the sixth game after saving a match point.

Nishikori, runner-up at the 2014 US Open, won the Court Two match on the second match point in the following game when Gulbis, now limping badly, hit a return long.