LAKE FOREST, Illinois (Reuters) - Jason Day rocketed out of the blocks on Thursday in his quest for world number one status and a fourth win in six starts, seizing a four-shot early lead in the opening round of the weather-hit BMW Championship.
Day, who could leapfrog Rory McIlroy and Jordan Spieth to reach the top of the rankings with victory this week, produced sizzling form as he moved to 10 under par after 17 holes before play was suspended for the day due to the threat of lightning.
That left the Australian world number three a commanding four strokes ahead of American Daniel Berger, who eagled his final hole, the par-four ninth, for a six-under 65 in breezy conditions at Conway Farms Golf Club.
Masters and U.S. Open champion Spieth was part of a four-way tie for third at five under as he tried to keep pace with playing partner Day in the third of the PGA Tour’s four concluding playoff events in the season-long FedExCup race.
Spieth was level with fellow Americans Brendon Todd, who returned a 66, Kevin Chappell, who had completed 16 holes, and Justin Thomas, after 13.
Day, who won the Canadian Open, PGA Championship and The Barclays in his last five starts, chalked up four birdies in his first six holes and though he gave a shot back on the 17th with a three-putt bogey, the 27-year-old then caught fire.
He birdied the 18th, holed out for eagle from a fairway bunker at the par-four first and added back-to-back birdies at the second and third to storm three strokes clear.
Day picked up further shots at the seventh and eighth to get to 10 under and raise hopes of a possible 59, then hit his tee shot at the ninth into the right rough before the siren sounded to halt the action under threatening skies.
Spieth was unable to keep pace with the red-hot Australian, despite registering a hole-in-one at the second and a chip-in birdie at the third, and was five under for the round after 17 holes.
World number one McIlroy was at three under after 12 holes in an elite field of 70 players from which just 30 will advance to the Tour Championship finale next week in Atlanta.
PGA Tour veteran Jim Furyk, who shot a 59 two years ago at Conway Farms in the second round of the BMW Championship, withdrew from the tournament with a wrist injury after completing just six holes in the opening round.
Editing by Mark Lamport-Stokes