EDMONTON, Alberta — Scott Dixon took another big step toward a second IndyCar championship today, holding off Helio Castroneves, his closest pursuer, for a victory in the Rexall Edmonton Indy.

Castroneves, still looking for his first win of the season, kept the pressure on Dixon lap after lap on the temporary airport circuit. But Castroneves nearly slid off course on worn out tires six laps from the end, allowing the New Zealander to cruise to his fifth victory of the season.

"I've got to thank the team," Dixon said. "We were struggling at the start of the weekend. We were probably at best about 11th. So, to come through is simply not what we expected. But my guys nailed that (last) pit stop and we got that lead and we were going to be unstoppable."

Castroneves led a race-high 35 laps and appeared to have the best car in the 27-car field most of the day. But Dixon, who had been running third behind Penske Racing teammates Castroneves and Ryan Briscoe, got past both of them during a pit stop under caution on lap 51.

Several other drivers, on different strategies, stayed out and were ahead at that point, but Dixon eventually inherited the lead when Tony Kanaan pitted on lap 62. The Indianapolis 500 winner then led the rest of the way.

Castroneves did his best to catch the leader until he locked up his brakes and skidded through turn one on lap 86. He recovered in time to stay in second, but fell too far behind to make another run in the race, scheduled to go 95 laps but cut four laps short by a one-hour, 50-minute time limit.

"Not only did he not make any mistakes, but he did what he had to do today," said Mike Hull, team director for Chip Ganassi Racing. "Scott drove a good, patient race with an Indy 500 champion like Helio behind him. That's a tough thing to be doing when that guy fills your mirrors."

Castroneves agreed.

"I was doing everything I could, pushing, putting pressure (on Dixon) until my tires just gave up," said the frustrated Castroneves, who finished second for the seventh time this season. "You know, he never made a mistake.

"I don't know what to do. I'll just keep working hard. It ain't over yet. It ain't over yet."

Dixon, who led the final 30 laps on the 1.973-mile, 14-turn circuit, began the day 58 points ahead of Castroneves and now leads the Brazilian by 65 heading into the race at Kentucky Speedway in two weeks.

But Dixon, the 2003 series champion who lost the 2007 title to Dario Franchitti when he ran out of fuel on the last lap of the last race, remains wary with four races to go. And he's still smarting from a mistake he made on the road course at Watkins Glen earlier this month when he spun himself out during a late caution and wound up finishing 11th instead of challenging for a victory.

"Last year, I think we didn't start the season as strong as we needed to," Dixon said. "This year, we definitely made sure that we did. And I gave myself a bit of a kick in the bum after what I did at Watkins Glen.

"So I think we got more motivation for myself and for the team, and you know we can't lose the championship now because, if I do, it will be because of that race."

Dan Wheldon, Dixon's teammate, lost ground when he and Oriol Servia collided late in the race, finishing seventh. The Englishman is third in the standings, 115 points behind Dixon.

It was the first IndyCar race at the former Champ Car venue.

Justin Wilson, one of nine drivers making the transition from the defunct Champ Car World Series to the newly unified IndyCar Series, finished third. Another former Champ Car star, Paul Tracy, making only his second race start of the season, finished fourth, followed by former teammate Oriol Servia and Briscoe.