Louis Oosthuizen and Rory McIlroy enjoy a joke. Rory McIlroy made six birdies in a 67 and was still made to feel like a man in reverse gear at the Deutsche Bank Championship in Boston.

The world No 1 looked on in frustration and admiration for a more than 90 minutes as playing partner Louis Oosthuizen made seven birdies in a row and eight in his first 10 holes en route to an eight under 63.

The South African leads by three shots from McIlroy with a tournament record 54-hole today of 19 under par in the second FedEx Cup event. Sponsored by FedEx’s big rivals UPS, Oosthuizen could steal some sponsorship thunder today if he holds of McIlroy and wins.

But McIlroy is playing with supreme confidence and having trailed by six strokes at one stage of the third round he emerged from the ordeal looking more dangerous than ever in his quest to make it to the Toru Championship with options of overall FedEx cup victory.

“You think going out with a one‑shot lead and shooting 67 that you might still be in the lead going into the last day.  But Louis put on a display out there for a few holes, reeling off seven birdies in a row.  I was delighted when I got the honour back on the 12th tee, but it was great to watch. 

“Louis is the sort of player that can do that.  He’s very explosive, and he didn’t really put a foot wrong today.  Very impressive round by him and very happy with my round, and very happy that I am still in touching distance going into tomorrow.”

McIlroy birdied the first two holes, missing an eight footer for eagle at the second as Oosthuizen started par-birdie and then went ballistic.

The man who shot a 57 around Mossel Bay 10 years go, birdied seven holes in a row from the fourth as Mcilroy cover the same stretch in one over par to go from two ahead to six behind.

Oosthuizen briefly entertained thoughts of a 59 on the front nine but his birdie run dried up and McIlroy kept his patience, birdied the 11th and 12th to cut the gap to four and then followed a bogey at the 15th with birdies at the 16th and 18th.

Oosthuizen finished bogey-birdie for his 63 to lead on 19 under with Tiger Woods (68) and US Ryder Cup wildcard hopeful Dustin Johnson (65) six shots behind on 13 under.

McIlroy certainly feels good about his chances of matching Woods by winning for the third time this season. At least, he knows he has enough patience not to panic.

McIlroy is feeling confident about his game for obvious reasons. “It’s hard not to look at the guy beside you making all these birdies and feel like you’re going backwards,” he said of Oosthuizen”s purple patch.  “But as I said, just stay patient and concentrate on yourself. 

“I thought if I went out and shot another solid score in the mid 60s like I did, I’d be in a good position going into tomorrow, and I still feel like I am in a good position, only three back.  I’ve come from further behind before.  It’s going to be an interesting day tomorrow.”

McIlroy has won four times in the US but only once has he come from behind. at the 2010 Wells Fargo at Quail Hollow he was four behind and won by four. 

As for Padraig Harrington and Graeme McDowell, they appeared to be playing a different golf course to the two leaders.

Both shots three over 75s to slip back to tied 77th in six over par - a mind-blowing 25 strokes off the lead.

Harrington, who turned 41 on Friday, had to hole a four footer for birdie on the 18th on Saturday  just to make the halfway cut. Yet he struggled with the blade again on Sunday, taking 31 putt

Playing his sixth event in nine weeks since the Irish Open at the end of June, he confessed on Saturday that his efforts to make the Ryder Cup team are starting to take a toll.

“I’ve just been flat this week,” Harrington told Golfweek. “There were a long four days into (the tournament) and my preparation has not been quite right. I’ve been pushing hard the last six, eight weeks.”

He looks certain to make the top 70 who qualify for next week’s third FedEx Cup event at Crooked Stick in Indiana but whether he has the energy to contend remains to be seen.

“I’m only a win away from being in the top five,” he said. “(Then) it doesn’t matter who you are, once you’re in the game (if you’re top five into the Tour Championship and win, you win the FedEx Cup), you still have a chance.”

McDowell will be hoping he rediscover some form ahead of the Ryder Cup. He hasn’t broken 70 in his last six rounds and appears to be struggling to hole putts.

“Ugly ball striking couple of days to make cut on number,” he tweeted after the second round. “Been focussing attention on short game lately, long game goes south.”