CROMWELL, Connecticut (Reuters) - American David Mathis shot a hole-in-one on his way to a one-stroke lead after Thursday's first round of the Travelers Championship.

Mathis started birdie, hole-in-one, birdie and rode that starting wave to a round of six under par 64 on the TPC River Highlands layout.

In search of his first PGA Tour victory, Mathis leads a group of three players - Sweden's defending champion Fredrik Jacobson, Australian Nathan Green and American Will Claxton - on 65.

The first round featured scorching temperatures near 100 degrees and a hot pairing of major champions with U.S. Open victor Webb Simpson playing alongside fellow Americans Bubba Watson and Keegan Bradley.

Masters champion Watson, a winner here in 2010, started his round with consecutive birdies and the back nine with an eagle on the par four 10th after holing out from 137 yards.

He finished at four-under 66 along with Simpson, who got to five under with a birdie at 15 but slipped back with a bogey at the next.

Bradley, winner of the 2011 PGA Championship, finished at two under.

(Editing By Alison Wildey)