Defending champion Henrik Stenson felt like he had "hit the wall" at the end of a long season, but still managed to claim the halfway lead in the DP World Tour Championship in Dubai.
Stenson, whose win at Jumeirah Golf Estates 12 months ago ensured he became the first man to win the Race to Dubai and FedEx Cup in the same year, added a second round of 66 to his opening 68 to finish 10 under par.
But the world number four has Open and US PGA champion Rory McIlroy just two shots behind alongside Scotland's Richie Ramsay and England's Danny Willett, with Ireland's Shane Lowry - aided by a hole-in-one on the 13th - and former US Open champion Justin Rose among a five-strong group another stroke back.
"There's still a lot of golf to play and I'm really happy with how I closed this round," said Stenson, who was 25 under par in winning by six shots last year.
"Around the 12th hole I felt like I was running out of steam. It was difficult mentally from there on. I had to really focus hard and drag myself over the finish line.
"It's hot and sticky and even though I'm drinking well and getting plenty of energy, I just felt like I hit the wall on 12. If it's one or two holes left, you normally feel like, 'okay, I can hang on'. But it was a bit of an uphill (struggle) from there. I managed to finish in good style anyway so I'm pleased with that."
Playing his first tournament after a six-week lay-off, McIlroy could only add a scrappy 70 to his flawless opening 66, carding four birdies, two bogeys and a par on the seventh after a mis-hit second shot with a five wood which he described as "a fat, low, duck-hook runner that was not intentional".
The world number one recovered from the shock of hitting that shot like a high handicapper and a bogey on the 12th with birdies on the 14th and 15th, only to three-putt the 16th and drive into the water on the last.
"I'm in a good position and there is a lot of golf left," McIlroy added. "I've definitely been in worse positions after two rounds and still won.
"It could have been worse but it probably could have been a little better. I definitely didn't have it like I did yesterday. I had to dig in a little bit so hopefully that's the bad one out of the way and I have 36 holes now to make some ground up on Henrik.
"Henrik's very comfortable on this golf course obviously. I can't let him get too far ahead tomorrow. I have to get off to a fast start and try and put a bit of pressure on him. Hopefully I can do that."
Lowry's hole-in-one, from 183 yards with a six iron, was his first on the European Tour and took him just one off the lead at the time, but the world number 52 was unable to pick up any further shots on the last five holes.
"It was a beautiful shot, a perfect number for my six iron," said Lowry, who needs a good finish to move into the world's top 50 and secure his place in next year's Masters.
"It's my first in tournament play and only my second ever so it was pretty exciting. It was hard to go on and play the next hole after that."
Speaking about his round of 71 after starting the day tied for the lead with McIlroy, Lowry added: "I am still in the tournament and I suppose if you had given me that on Thursday I would have taken it."