A 68, following on from yesterday’s opening 69, left the Dubliner five under par and four shots off the lead after Australian John Senden’s flying start to his second round.
Harrington, waiting on Montgomerie’s wildcard selections to discover if he will compete at Celtic Manor, said: “After missing the cut in the (USPGA) the last thing I wanted was to come here and miss the cut-off or play poorly and then say, well, maybe I’m out of form.
“I believe that Monty should make a decision based on the full year and who is going to play consistently and who we can rely on to play well. But in the last tournament of the year, a couple of days before the team is going to be picked, it’s nice to be showing a bit of form. It won’t do me any harm. It’s no burden to carry it, let’s say.”
Six birdies more than cancelled out his three dropped shots to boost his bid for victory in the opening event of the FedEx Cup series, although he admitted: “I should be better than five under par myself.
“But it’s neither here nor there, if it stays within a few of the lead that’s fine. I’m in position to (challenge) as long as nobody runs away with it.”
Senden looked in the mood to do just that as he birdied four of the first five holes, reaching eight under par and moving a shot ahead of Kevin Streelman.
World number one Tiger Woods, the joint overnight leader, slipped back after a second round of two over par 73, which contained four bogeys on his second nine, after he started on the 10th.
Streelman, one over par after the first round, produced a superb round of 63 to fire himself into contention. Having also started on the back nine, he had a run of six birdies in seven holes from the 18th to thank for his surge up the leaderboard.
Stewart Cink shot 69 to sit a shot further back, level with Brian Gay after the latter birdied the third and fifth but bogeyed the seventh.
Webb Simpson carded a 65 featuring nine birdies to race to five under, but Adam Scott was unable to build on his opening 66 as a level-par 71 left him on the same mark.
England’s Paul Casey, another awaiting Montgomerie’s call, was four under after a second successive 69.