LAKE FOREST, Ill. — Only the weather could stop Jason Day at the BMW Championship on Thursday.

Day began his latest quest to reach No. 1 in the world by holing out from a fairway bunker for eagle and powering his way to nine birdies.

The PGA champion was 10-under par through 17 holes when the first round at Conway Farms was halted because of approaching storms.

Day had just hammered a tee shot 346 yards with the wind at his back, leaving him 44 yards to the hole at No. 9. He needed to hole that shot for a 59, and he had to wait until Friday morning for that. The round was to resume at 7:30 a.m.

He was four shots ahead of PGA Tour rookie Daniel Berger, who finished his round at 6-under 65.

Day was walking to the sixth green when someone said in an exchange of greetings, “How are you doing, Jason?” This caused Jordan Spieth to turn around and say with a smile, “Really? You’re asking him that?”

Spieth had a hole-in-one and followed with a chip-in from 80 feet for birdie to get his game on track. He was at 5 under.

But as he walked to the fourth tee, he pointed behind him and said of Day, “He’s still the clinic. I’ve barely got the (honors on the) tee.”

The 27-year-old Australian was as sharp as he has been all year.

It was the best show of the PGA Tour’s postseason, even for a Thursday that was interrupted by a dark and stormy sky north of Chicago.

The group of Day, Spieth and Rickie Fowler – Nos. 1-2-3 in the FedEx Cup – attracted an enormous gallery and the players delivered one great shot after another.

Fowler, coming off his third win of the year at the TPC Boston two weeks ago, must have felt like a third-wheel at the end, though he produced four straight birdies on his front nine.

When they made the turn, the hits kept coming.

Day’s shot from 79 yards in a fairway bunker on No. 1 landed beyond the hole and spun back a few feet for eagle to get him to 6 under.

On the par-3 second, Spieth’s tee shot just covered the bunker, hopped once in the first cut and rolled into the cup for an ace, the second of his PGA Tour career. Day holed a 20-foot birdie putt.

Both made birdie on No. 3, Spieth with his long chip-in and Day with a wedge to 5 feet. Spieth found his groove with a shot into 4 feet on No. 3 for another birdie.

Day’s power was evident on the 600-yard eighth, into a strengthening wind. He hit his tee shot 305 yards, and then hit 3-wood high and into the wind just over a bunker to the collar of the green. His chip for eagle narrowly missed.

ITALIAN OPEN: Belgium’s Nicolas Colsaerts had eight straight birdies and finished with a 9-under 63 to take the lead at Monza, Italy.

Italy’s Francesco Molinari was tied for second at 65 with Sweden’s Kristoffer Broberg and India’s Shiv Kapur.

Molinari won the event in 2006 at Castello di Tolcinasco.