Not satisfied having reached that goal, Murray withstood his toughest test of the tournament and defeated Del Potro 6-7 (4), 7-6 (3), 6-1 Sunday.
"I love winning tournaments, it's great, and every player will tell you the same thing," Murray said.
"But it's tough because I've never been to No. 2 in the world before, so that's new to me. I've won a couple of Masters Series [events] now, and it still feels great. But getting to No. 2, maybe because it's something different it means a little bit more."
The 22-year-old from Scotland was assured before the final of leapfrogging Rafael Nadal into the second spot when the ATP Tour rankings are released Monday. The victory gave Murray an additional 400 ranking points to get him to 9,250 compared to 11,040 for world No. 1 Roger Federer and 8,665 for Nadal.
The third-seeded Murray matched his career best from last season with his fifth tournament win of the year and improved his record to 11-4 against top-10 players this season.
He took time off to train in Florida after a bitterly disappointing loss to Andy Roddick in the semifinal at Wimbledon, and Murray couldn't have drawn up a better return to the court.
"It's a perfect way to come back," he said. "It goes one of two ways. Losing to Roddick, there's no shame in that to start with. I could have gone away and become a worse player and not work on anything, or go and practice harder and become better so the same thing doesn't happen the next time around."
Del Potro, from Argentina, was looking for his second straight tournament victory after winning in Washington, a week earlier. He squandered an opportunity to jump past Roddick into fifth in the world rankings.
The match turned when Del Potro called for the trainer to work on a sore shoulder while up 6-5 in the second set. After the medical timeout, Murray held serve at love and won the tiebreaker.
Del Potro said he still hasn't reached the point where he can consider himself to be in the same class as Murray, Nadal or Federer.
"I need to work hard to be like them," Del Potro said. "I can play against them, but I need to improve my game a lot if I want to be top-four, or top-two or No. 1."
Del Potro left the court for several minutes following that second set and was clearly not the same player upon his return, falling behind 4-0 in the third set. Del Potro did break Murray to get it to 4-1, but called for the trainer again before Murray broke Del Potro to go up 5-1 and then serve out the match.
Del Potro said a combination of that nagging shoulder injury, the physical strain of playing nine matches in 13 days and the stifling heat Sunday in Montreal was too much for him to overcome physically.
"I was so tired [in the third set]," he said. "I had my chances in the second set tiebreak, but I didn't take them."
After needing 2 hours, 17 minutes to play the first two sets, Murray needed only 25 minutes to win the decisive third set.
"Before the match I felt like I was probably going to be physically stronger," Murray said. "He was obviously tired [in the third set] and I made a lot of returns which I hadn't really been doing. His serve slowed down a little bit and I made more returns. I served well at the beginning of the third set to make sure I stayed ahead, and that was the only difference."
The tightly contested match under hot, muggy conditions pleased the sellout crowd of 11,490 at Uniprix Stadium, bringing the total attendance for the event to 200,077. That broke the attendance record for a one-week ATP event of 185,252 set here in 2007.
Murray didn't drop a set in the tournament -- his first since Wimbledon -- until Del Potro won the first set Sunday in a tiebreak.