Roger Federer is now the 3/1 favourite to win the Australian Open for a fifth time.
The Swiss overcame Kei Nishikori in five sets, in a match lasting three hours and 24 minutes, to reach the quarter-finals in Melbourne.
He will now continue his pursuit of an 18th grand slam title against Mischa Zverev, the world number 50 who pulled off a shock win over top seed Andy Murray.
Federer is 1/12 to progress to the last four with Zverev 7/1 for another upset while there are odds of 32/25 for the match to have more than 3.5 sets.
The hard-fought victory over Nishikori came in what was only Federer’s fourth official match since returning from six months out with a knee injury.
Federer, 35, has warned his rivals he feels fit and ready to go the distance, saying: “I felt great in the fifth, I must say. Even deep into the fourth I thought 'Yeah, fifth, here we go, no problem for me. I'm feeling good about my chances'.
"I was playing positive tennis, I was playing offensive. My body was reacting. I was playing way better than the first couple of rounds where I put in a lot of mental energy to stay with my opponents, figure them out, how were they going to play, how were the conditions going to be - understanding the comeback really.
"I was able to focus point per point on my opponent, on the tactics. That didn't drain me much. I felt great in the fifth, which I'm very happy about."
This is the 49th grand slam in which Federer has reached the last eight while Zverev's quarter-final will be his first.Federer is 7/1 to prevail in a deciding set with Zverev 24/1 to do likewise and 7/2 to take the opening set.
Murray's loss, coming three days after Novak Djokovic's defeat to Denis Istomin, has thrown the draw wide open, with the likes of Federer, Milos Raonic, Rafael Nadal and Stan Wawrinka all primed to capitalise.
Wawrinka, the 2014 champion, faces Jo-Wilfried Tsonga in the quarter-finals after beating Italian Andreas Seppi in straight sets, all three going to a tie-break.
The fourth seed, 13/4 for more Melbourne glory, is 5/8 to get past the Frenchman, who is 32/25 to stay on course to reach a second Australian Open final after his feat in 2008 when going down to Djokovic.