The Jason Day train rolls through Chicago

The birdie put Day at 10-under par with one hole remaining, and moments after he hit his tee shot on No.

THE DAY TRAIN: Day still has one hole to play in his opening round at the BMW Championship, but this number speaks to his play over the last two months.

Day already was four shots clear of Daniel Berger with one hole to play 44 yards away for his second shot on No.

THE BANTER: Day and Spieth have played the opening two rounds together in all three of these FedEx Cup playoff events, and they were paired in the final round of the PGA Championship.

Spieth made a hole-in-one on the second hole, and Day calmly poured in a 20-foot birdie.

On the next hole, Spieth chipped in from 80 feet, and Day rapped in a 5-foot birdie.

On the next hole, Day pounded a driver at the 352-yard seventh green and came up about 30 feet short.

THE STRETCH: Day and Spieth lit up Conway Farms even as the storms moved closer, especially on the first and second hole.

Day holed out from 79 yards in a bunker for eagle on the first hole.

Spieth chipped in from 80 feet on the third hole, and Day made birdie with a 5-foot putt.