But he was back to attacking on his final two match points, rushing the net on the sixth after his serve, only to be trumped by a passing shot combination from Federer. On the seventh and last, he came forward again, but his chipped backhand approach shot on the run failed to clear the net.
“I could have blinked at the wrong time and shanked,” Federer said. “That would have been it.”
Instead, he is back in the semifinals of the Australian Open, where — spare a thought for Federer — he will face Djokovic, a seven-time champion here, on Thursday night.
Federer’s draw, which looked like a breeze on paper, has instead been a prolonged great escape. He also trailed, 4-8, in the fifth-set tiebreaker against John Millman in the third round before winning the final six points.
Djokovic lost his first set of the tournament, against Jan-Lennard Struff, but has yet to drop another. He defeated Milos Raonic, 6-4, 6-3, 7-6 (1), in their quarterfinal on Tuesday night. Djokovic complained about being unable to see well at times under the lights, and changed contact lenses late in the third set. But he was still able to break Raonic’s fearsome serve twice and run his record against the Canadian to 10-0.
At age 32, he should be fresher than Federer, despite leading Serbia to victory in the new ATP Cup team event before the Australian Open. Federer skipped the event to preserve his energy and family time, arriving early in Melbourne and playing practice matches.
But he has blown hot and cold, often struggling with his forehand consistency. Against Sandgren, he said, he began feeling pain in the groin muscle in his left leg in the second set and eventually sought treatment.
Federer planned to undergo medical tests on Wednesday, but if he is able to play, Djokovic will deservedly be the solid favorite in their 50th match.