Roger Federer is braced for a John Isner bombardment, with the 20-time grand slam champion comparing his upcoming showdown against the big-serving American to a goalkeeper in a penalty shoot-out.

Former world number one Federer reached his fifth Miami Open final in merciless fashion as the Swiss star outclassed teenager Denis Shapovalov 6-2 6-4 on Friday.

Federer was irresistible under the Miami lights, the three-time champion producing a masterclass to set up a clash with seventh seed Isner in the ATP 1000 tournament decider.

The fourth-seeded Federer knows what to expect against Isner as he likened Sunday's looming contest to a football shoot-out.

"I know what to expect. He will not miss many serves. He's got an amazing serve, one of the best ever in the game," Federer said during his on-court interview.

"It's really hard to play against him. I'm a big fan of his. I actually really enjoy watching him play.

"I love it, I honestly love big servers. To watch them, [wondering] if they are going to ace every second or third point.

"For me that's exciting because it's like penalty shoot-outs in soccer. I'll be the goalie on Sunday and try to get as many balls back as possible."

Shapovalov – the 19-year-old Canadian – was no match for Federer in their first career meeting, despite his best efforts.

"Tough loss but it was enjoyable to be out there with your idol on the court," Shapovalov said. "It was kind of surreal. I did what I could...He's got every shot mastered. I don't think he has any weaknesses. That's why he's the greatest of all time."