Jack Sock thinks Roger Federer is the best tennis player in history, but that doesn't mean the 18th-ranked American is discounting his chances against the Swiss great in the Indian Wells semi-finals.
"In my opinion he's the best to ever play. It will definitely be a challenge," Sock said after ousting world number five Kei Nishikori 6-3, 2-6, 6-2 on Friday.
Sock notched his first victory over a top-five player, and reached the semi-finals of an elite Masters series event for the first time.
But with two titles to his credit already this season Sock says he's a much improved player from the one who lost to Federer in two prior meetings, both in 2015.
Sock called Federer's 18th Grand Slam triumph at the Australian Open in January a "testament" to Federer's ability, after the Swiss missed some six months of 2016 through injury.
But he also noted that Federer was shocked by 116th-ranked Evgeny Donskoy in Dubai this month.
"The trend of tennis now, is a guy who is playing well at any ranking can give any guy trouble," Sock said.
"When I played him here last and I played him in Basel a couple years ago I don't think I went on the court giving myself a ton of chances of winning. I think that's changed, for sure.
"Obviously he's playing incredible tennis not only this year but this week," Sock added. "But on the flip side of that, I am playing confident tennis as well myself. And I think if I go out there and play the right tennis and play the right strategy, I think I can give myself a shot, for sure."
Sock, who withstood four match points against Grigor Dimitrov in the third round and had another close shave against Malek Jaziri in the fourth, used his high kick serve and powerful groundstrokes to overcome Nishikori -- who hadn't dropped a set in his three prior matches.
"Kick serve, especially on these courts, is deadly for me," Sock said. "So that was a big part of the game plan for me today going in.
"If Kei is hitting the ball in the strike zone he is going to beat pretty much anyone in the world on any given day.
"For me, it was all about trying to get him out of that slot and let him not be taking balls at his hip and waist and dictating play. So the kick serve for me today was crucial, first and second serve, and that's why I used it a lot."
Nishikori was left regretting too many loose points, and a slow start that let Sock leap to a 3-0 lead in the opening set, in which one early break proved all he needed.
While Nishikori played better in the second to level the match, he dropped the first game of the third set to again concede the advantage.
"I don't think I played good enough to beat Jack today," Nishikori said. "I think there were too many unforced errors and I wasn't playing aggressive enough to get more chances."