Sam Ryder and Kevin Tway share clubhouse lead as darkness curtails play at Houston Open

Fellow countrymen Lucas Glover and Tway are a shot behind on seven under having completed their rounds, while Beau Hossler has the same score through 16

The American is sitting at the top of the leaderboard in Texas (Getty)

Sam Ryder birdied four of six holes on the back nine - but was unable to complete his first round at the Houston Open due to darkness.

The American is sitting at the top of the leaderboard in Texas on eight under after carding a 32 on the front nine.

Fellow countrymen Lucas Glover and Kevin Tway are a shot behind on seven under having completed their rounds, while Beau Hossler has the same score through 16.

A group of five sit a shot behind that, including Ireland's Paul Dunne.

Phil Mickelson - 43-time PGA Tour winner - shot a 30 to start his week, helped by an approach shot within five feet on the par-5 4th.

But the form did not continue into the back nine where he double bogeyed the par-3 14th and sits tied for 26th on four-under along with Justin Rose.

Defending champion Russell Henley carded a 69 to sit tied for 48th.

The first round will resume at 7.20am on Friday.