Pádraig Harrington admitted winning the season-long Charles Schwab Cup could be "a long shot" now after a "relentless" Steven Alker remained one clear of the Dubliner in the Charles Schwab Cup Championship in Arizona.

Harrington must win the season-ending event and hope Alker finishes outside the top five if he's to overtake the New Zealander in the points list and win the $1 million bonus.

But it's looking like mission impossible so far after Harrington made eight birdies and a bogey in a seven-under 64 at Phoenix Country Club but could only match Alker's bogey-free effort and remain one stroke behind the Kiwi with two rounds to go.

Scores

"Look, he's playing very well," said Harrington, who played with Alker on Thursday and will play with him again in the final group today. "I've played with him every week in the Playoffs at this stage and he's not backing down. He won one of the Playoffs (the Dominion Energy Charity Classic), he's finishing the season really strong. He's not limping home in any shape or form.

"He started great, but he's finishing very strong. You couldn't begrudge him where he is at the moment, you couldn't begrudge him winning this outright, but I'll try and do that the best I can."

Alker and Harrington go into today's third round in the final group, with the New Zealander one ahead of the Irish star on 13-under par.

Retief Goosen and Brian Gay are tied for third at 10 under, but it looks like a two-horse race with Alker a strong front runner after hitting 25 of 28 fairways over the first two days and making 13 birdies and no bogeys.

Given those numbers, Harrington has decided to focus on winning the tournament rather than worrying about where the "relentless" Alker might finish.

"I had a putt about 12 feet on the fifth to go 5 under after five and I didn't hole it, but 4 under, going well," said Harrington, who followed a three-putt bogey at the 16th with two closing birdies, leaving a 25-foot eagle putt a foot short at the 18th.

"I look up, and Steve is just right there and I go, I started as well as I could and I still can't get away from him.

"Steve is doing a great job. I'm trying to mind my own business most of the time doing my thing out there and I've got another 36 holes to do that.

"It seems that the Schwab Cup could be a bit of a long shot at this stage, but I'm very much in the tournament and that's what we're going to focus on now."

Alker has won four times this year and knows he has to keep going right to the finishing line with Harrington showing no signs of going away.

"Well, I know what I've got to do, the numbers are all there," Alker said. "It's kind of black and white. I just try and put myself in position to win a golf tournament, that's big for me. Yeah, he played well today, so I've got to keep hammering those birdies out."

Darren Cklarke is tied for 21st on three-under after a level par 71 yesterday.