Patrick Reed made four birdies in a row around the turn to open up a one-shot lead on a thrilling second day of the DP World Tour Championship, Dubai.
The American was five under for the day through 11 holes to get to eight under and lead the way from a seven-strong group in second that included Race to Dubai chasing Tommy Fleetwood and four-time Major Champion Rory McIlroy.
Swede Alexander Björk was the clubhouse leader at seven under after a brilliant 65, with Dean Burmester, Wade Ormsby, Matt Wallace and Jordan Smith also in the chasing pack at the season's eighth Rolex Series event.
Fleetwood needs a win this week at Jumeirah Golf Estates to have a chance of successfully defending his Race to Dubai title and he remained bogey-free for the week after 12 holes.
A top five for Francesco Molinari would see him win the season-long crown regardless of Fleetwood's finish and he was four shots off the lead at four under.
Ormsby made a birdie-birdie-birdie start to join overnight leaders Smith and Adrian Otaegui at six under, and Burmester's fifth birdie of the day on the tenth made it a four-way tie.
Wallace holed a long putt on the first and took advantage of the par-five second to also hit the front but they were soon all leapfrogged by Björk who carded the lowest round of the week so far.
He made birdies on the first, second, sixth and eighth with a bogey on the fourth to turn in 33, and then added further gains on the 12th, 14th and 16th with a dropped shot on the 13th.
That had him one off the lead but he holed a monster eagle putt on the par-five last and jumped into the lead.
Smith birdied the second to join the lead, with Ormsby capitalising on the par-five seventh and Wallace putting an approach to four feet on the fifth.
McIlroy and Reed were playing together and putting on a show reminiscent of their singles battle at the 2016 Ryder Cup.
Reed birdied the second but McIlroy was producing the early fireworks, putting his approach to four feet on the first, birdieing the second but then three-putting the third.
He almost aced the sixth and grazed the edge on the seventh and eighth - where Reed made a birdie from 15 feet - before both players hit stunning approaches into the ninth and tenth.
Fleetwood was a picture of consistency and he holed a 30-footer on the first and an 18-footer on the eighth to turn in 34.
Approaches to inside ten feet on the tenth and 11th then had him in a share of the lead and Burmester made it an eight-way tie with a birdie on the 14th.
A six-footer from Reed on the 11th then brought a fourth birdie in a row and he broke out of the pack.
Henrik Stenson and Otaegui were six under.
