It proved pivotal as the South African recovered to win 2-6 6-7 (5-7) 7-5 6-4 13-11 in four hours and 13 minutes.
But, turning 37 in less than a month, Federer refused to blame fatigue after giving up a two-set advantage for the first time since doing so seven years ago against Jo-Wilfried Tsonga and Novak Djokovic at consecutive slams at Wimbledon and the US Open.
Wilander says Isner, who has finally put together a run at Wimbledon, could be the dark horse in the last eight.
However, Federer has held all of his 55 service games this year and last dropped serve in the semi-finals in 2017 - 81 service games ago.
"I feel like a lot of aspects of my game can give him a lot of trouble", said Anderson, the first South African man in the Wimbledon quarter-finals since Wayne Ferreira in 1994.
Roger Federer suggested a clash between the World Cup final and the Wimbledon men's singles final may be more of a concern for those in Russian Federation rather than competitors at SW19.
Tendulkar then invited Federer to "exchange notes" after the tournament's end, which the eight-time Wimbledon champion courteously accepted.
"I will watch Wimbledon from home, hoping for Rafa's win", Toni added. Federer has won all four of the previous head-to-head matchups, most recently taking down Anderson 6-1, 6-1 at the 2015 Cincinnati Masters.
"The more I can just treat it like another tennis match, the better for me".
"Not only did he battle back from two sets to love down, but it was an overwhelming performance in the opening set from Federer where Anderson didn't really get a look in".
"It was crucial for him to stay in the match at the beginning of the second set and then it got tougher", said 20-time major victor Federer.
Serbia's Djokovic shrugged off a second-set slump to reach a Grand Slam semifinal for the first time since 2016 by beating the Japanese 6-3, 3-6, 6-2, 6-2.
Serbia´s Novak Djokovic serves to Japan´s Kei Nishikori during their men´s singles quarter-finals match on the ninth day of the 2018 Wimbledon Championships. I think it went in spells a bit also, how I was able to return his serve.
"Do you think I ruined the court?" he bellowed at Ramos.
While England will be gearing up for its biggest match of the day - the World Cup semi-final involving the Three Lions and Croatia, London will play host to some exciting quarter-final action of Wimbledon 2018.
He forced a tiebreak but, despite losing the first mini-break, Federer turned things around to go two sets ahead.