With his win, Murray will vault past Spain's Rafael Nadal into a career-high second in ATP rankings behind No. 1 Roger Federer of Switzerland when the next rankings are released on Monday. Nadal, returning from a knee injury, lost in the quarterfinals Friday night.
Murray ousted the seventh-seeded Tsonga 6-4, 7-6 (8).
Del Potro beat Roddick 4-6, 6-2, 7-5. He also defeated the fifth-seeded American in a third-set tiebreaker in the final of a tournament in Washington on Sunday.
Roddick used a service break to take his opening set, but was dominated in the second by the thorough baseline playing and serving of the 20-year-old Del Potro.
The two held service at 5-5 in the third, when Roddick went down 30-40 and then double-faulted. The 2003 Rogers Cup champion slammed his racket down on the court and the sixth-seeded Del Potro then served out the match.
"That was the worst game I've played in a while," Roddick said. "I won't forget that.
"I'm very disappointed with the way the match finished, as far as preparation for the U.S. Open, which is the point of this swing, I feel good about how I played. I like where my game is heading."
"These two weeks have been tough but it's a chance to win another tournament," Del Potro said.
"It will be good for me," he said. "I like playing players who are better than me. "I think he will have the pressure, but I have to play my best."
Murray is looking forward to becoming the new world No. 2.
"In terms of rankings, that's the biggest step I've taken so far," Murray said. "I played consistently well this year. ... Rafa had an injury, but it was Wimbledon that he missed.
"I also took a big break after Wimbledon. ... I've done enough to justify being No. 2. And getting close to one day becoming No. 1 is one of my goals. So it's great. I've put in a lot of hard work to get to this stage."
The 22-year-old Murray has a chance to become the first British player to win the event formerly known as the Canadian Open. The last Briton to reach the final was Roger Taylor, who lost in 1970 to Rod Laver.
Murray, already the highest-rated British player since ATP rankings were introduced in 1973, is the first person other than Nadal or Federer to hold the No 2 spot since July 18, 2005, when Lleyton Hewitt was second behind Federer. Murray has 8,850 points, 185 more than Nadal.
"Five years it's been Rafa and Roger as No. 1 and No. 2," Murray said. "Novak (Djokovic) had one or two matches to get to No. 2, so it's a tough thing to do because Rafa and Roger are maybe the best two of all time. So yeah, it's pretty special to get in between them."
Nadal was playing his first tournament since the French Open in May due to tendinitis in both knees. He said this week he still has work to do to reach his top level of tennis.
Murray also tied Djokovic for the lead in match wins this year with 49, including tournament victories in Doha, Rotterdam, Miami and the Queen's Club in England.
Murray broke service and held a 5-2 first-set lead when the streaky Tsonga broke back and threatened to tie it before the Scotland native served out the set.
The second set went to a tiebreaker in which Murray fought off two set points and finally won the Frenchman hit a backhand into the net.
Tsonga was coming off a dramatic three-set victory over Federer in which he trailed 5-1 in the third set only to rally and win in a tiebreaker.
"It's always tough against him because he dictates what happens in the match because of the way he plays," Murray said. "I just had to stay solid and make enough balls for him to make a few mistakes, and I came up with a few big returns."
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