TORONTO (Reuters) - Swiss second seed Stan Wawrinka won a hard-hitting battle with American Jack Sock on Thursday to reach the quarter-finals at the Rogers Cup with a 7-6(3) 6-2 triumph.

Wawrinka and Sock held serve throughout the first set to force a tiebreak that was won easily by Wawrinka who went on to dominate the second set where he charged out to a 4-0 lead and dropped just five points on serve to take the match.

Next up for the two-times grand slam champion is unseeded South African Kevin Anderson, who rallied to a 4-6 6-3 6-4 upset win over No. 12 seed Bernard Tomic of Australia.

Japanese third seed Kei Nishikori had little trouble getting by American Rajeev Ram as he needed just 68 minutes to register a convincing 6-3 6-4 win.

"The first set I played really good tennis. I had some tough times, but this score shows I was dominating a little bit," said Nishikori.

"I'm still not 100 percent yet, but feeling pretty strong. We'll have to see after a couple of more matches, but right now I feel good."

A confident Gael Monfils extended his recent run of form with a 7-6(5) 2-6 6-4 upset over Belgian seventh seed David Goffin to book his spot in the quarter-finals.

The 10th-seeded Frenchman, who arrived in Toronto fresh off earning his first tournament win in two-and-a-half years, will play either Canadian fourth seed Milos Raonic or American qualifier Jared Donaldson in the last eight.

(Reporting by Frank Pingue; Editing by Andrew Both)