Second seed Milos Raonic relied on his powerful serve to blast his way through his quarter-final match against American Steve Johnson at the Citi Open in Washington.

Wimbledon semi-finalist Raonic took a while to get going but was unstoppable once he found top gear, pounding down 16 aces to beat the unseeded Johnson 7-6 6-2.

The Canadian will meet another unseeded American, Donald Young, in the semi-final after Young upset seventh-seeded South African Kevin Anderson 3-6 7-6 6-2.

Raonic had a stern test against Johnson, who beat two other big men, American John Isner and Croat Ivo Karlovic, to reach the last eight.

Up against another powerful server, Johnson looked the more impressive in the first set, holding serve with ease.

But neither player could prise out so much as a break point and once Raonic won the tiebreak 7-2, he dominated the second set, twice breaking Johnson to close the match out in just under 80 minutes.

“It’s tough after a few weeks off but I’m happy with the way things are going,” said Raonic, who got within one match of the Wimbledon final before losing to Roger Federer.

“My attitude and mentality have been getting me through a lot of important stages.”