MONTREAL (REUTERS) - Argentinian Diego Schwartzman provided the day's biggest upset at the Montreal Masters when he took down third seed Dominic Thiem in a nearly three-hour battle on Tuesday.
Schwartzman climbed out of a 5-2 deficit in the decisive set, repeatedly escaping trouble, to win five straight games and pull off the victory 6-4, 6-7 (9-7), 7-5.
The world No. 36 had defeated 16th-ranked Roberto Bautista Agut earlier in the year and pushed Novak Djokovic to five sets at the French Open, but his win over Thiem is his biggest win of the season.
Thiem made eight double-faults in the loss.
Earlier, American Sam Querrey overcame a sluggish start to defeat Frenchman Vincent Millot 4-6, 7-6 (7-4), 7-5.
The battle was the second meeting between the pair in a week after Querrey defeated Millot in straight sets at the Los Cabos Open on Thursday, a tournament the American won.
The 29-year-old Querrey staved off the upset bid by the 31-year-old Millot, despite moving sluggishly around the court and his trusty first serve not being its usual lethal weapon.
His frustration boiled over early in the third set of the ATP 1000 event when he destroyed his racquet after having his service broken, but he won the next four games after the outburst.
Querrey will face another Frenchman, Jo-Wilfried Tsonga, the 2014 champion, in the round-of-32 on Wednesday.
Emerging Canadian Denis Shapovalov defeated Brazilian Rogerio Dutra da Silva 4-6, 7-6 (10-8), 6-4 in a thriller.
Backed by a home crowd that included Canadian National Hockey League Hall of Famer Wayne Gretzky, the 18-year-old staved off four match points in the second set before taking it in a tiebreaker.
"The fans really carried me. It was so fun to be out there on the court, it was so loud and energetic," Shapovalov said.
"It's a huge win. It gives me a lot of confidence and a lot of experience."
Shapovalov, who won the junior Wimbledon title last year and was granted a wildcard to the main tournament this year, faces the big-hitting Argentine Juan Martin del Potro in the second round.
In other matches, Belgian David Goffin and Spaniard Pablo Carreno Busta prevailed in their respective three-setters, and American Jack Sock beat Pierre-Hugues Herbert in straight sets.