Rory McIlroy improved his prospects at the WGC-FedEx St Jude Invitational with an encouraging bogey-free 67 to lie five shots behind the leader Matt Fitzpatrick at the half-way mark.
A week on from missing the cut at the Open Championship, McIlroy is determined to make amends in Memphis and his second round saw him make birdies at four, ten and 16 to leave him at four under.
Fitzpatrick shot 64 on Friday to take a two-stroke lead.
Sheffield-born Fitzpatrick, a five-time winner on the European Tour who finished second in March's Arnold Palmer Invitational on the PGA Tour, got his round off to a flier with four successive birdies.
Key to that was the quality of his iron play, and although he dropped a shot at the par-three eighth, he had two more birdies coming home to lift him to nine under.
He looked like being caught by Horschel, who started on the back nine with two birdies, before a bogey, an eagle and two further birdies put him within one of the lead until he dropped his second shot of the day at the par-four ninth to card a 66.
Overnight leader Jon Rahm, after his brilliant opening 62, salvaged his round with a late flourish after four bogeys in 15 holes.
Back-to-back birdies at 16 and 17, added to the earlier one at the 13th, saw him sign for a one-over 71 but still remain in contention at seven under along with Horschel, fellow American Patrick Cantlay and Australian Cameron Smith.
English duo Ian Poulter and Justin Rose and four-time major winner Brooks Koepka are at five under.
Tom Hoge topped the leaderboard as the weather again stopped play in the second round of the Barracuda Championship.
The 30-year-old mixed five birdies with two bogeys at the Montreux Golf and Country Club for an overall score of eight for his second round and a total of 21.
The tournament in Reno uses the Modified Stableford scoring system, which allocates points based on the number of strokes taken at each hole.
Ireland's Seamus Power is in a tie for 16th spot with a score of 15, but Padraig Harrington on a score of 4 will miss the cut.
Beau Hossler, John Chin and Collin Morikawa were tied for second on 20 points, one point behind Hoge.
Hossler recovered from two bogeys to make seven birdies - including three straight through holes 11 to 13 - adding 12 points to his first-round score of eight.
Chin moved up 13 places with a second-round score of 11, while Morikawa made four birdies and a bogey for a score of seven.
Scotland's Martin Laird was in a five-way tie for ninth on 17 points after cancelling out a bogey on the par-four fourth with an eagle and four birdies.
Several players had yet to start their second round when play was suspended in Nevada, with overnight leader David Lingmerth the best of those whose round was interrupted on 17 points through four holes.
Under the Modified Stableford scoring system, eight points are awarded for an albatross, five for an eagle, two for a birdie, zero for a par, minus one for a bogey and minus three for a double bogey or worse.
