ST. PETERSBURG, Russia - Canada's Milos Raonic won the St. Petersburg Open on Sunday with a gruelling three-set victory over Joao Sousa in the final.

The big-serving Raonic, seeded second, hit 22 aces as he held off stern pressure from Sousa to wrap up a 6-3, 3-6, 6-3 win.

The Thornhill, Ont., native dominated the first set, but lost a thrilling second in which Sousa saved seven break points in his first two service games before becoming the first player to break Raonic's serve at the St. Petersburg tournament.

Raonic went a break up on seventh-seeded Sousa's first service game in the decider and saved six break points on his own serve as he held on for the win.

Raonic's first title since the Washington Open in August 2014 strengthens his slim hopes of reaching the ATP Finals. He is now No. 9-ranked but is well behind the top eight in the year-to-date ranking used to determine tour finals qualification.

Raonic is now 7-8 in tour finals, while Sousa drops to 1-5, without a win since his first final at the 2013 Malaysian Open.

Earlier Sunday, Treat Huey of the Philippines and Henri Kontinen of Finland won the St. Petersburg doubles title, beating the Austrian duo of Julian Knowle and Alexander Peya 7-5, 6-3.

The St. Petersburg Open is a $1 million hard-court event that returned to the ATP calendar this season following a one-year absence. The tournament was moved to Israel last year but that event did not take place due to violence in the Gaza Strip.