The 32-year-old half-back looks set to end his 16-year career with the Black and Whites at the end of the season after being told he will not get a new contract, but he showed he still has plenty to offer as he engineered an impressive win for his side at the KC Stadium.
Horne, who returned to the side in place of the injured Jordan Rankin, scored their first try and was influential throughout as lowly Hull maintained their recent improvement by claiming a notable scalp.
St Helens captain Paul Wellens scored his 1,000th point for his club as they battled throughout with a makeshift half-back pair, but they can have no complaints over the outcome.
Saints, whose only other defeat in their last seven matches was at neighbouring Hull KR, stay top courtesy of Leeds’s surprise home defeat by Bradford and also lift the Steve Prescott Cup in memory of the former England full-back who played with distinction for both clubs after topping the aggregate score in the two games this season. Saints were the liveliest team in a nervous opening quarter and took the lead when winger Tom Makinson scooped up a wayward pass and wrong-footed the Hull defence.
Mark Percival added the conversion but Hull gradually clawed their way back into the contest, largely through the efforts of Horne. He twisted and turned out of a series of attempted tackles to register his side’s first try on 17 minutes and Joe Westerman levelled the scores.
The introduction of heavyweight forward Iafeta Paleaaesina further lifted the crowd as he tore into the Saints defence.
Six minutes before the break winger Tom Lineham forced his way over and Westerman’s second goal made it 12-6.
After the break Makinson demonstrated his ever-present threat with a 50-metre break out of defence and, although Jamie Shaul pulled off a crucial tackle, Hull’s defence was exposed out wide and Wellens went over for his side’s second try.
Percival’s second conversion tied the scores but that served to inject fresh enthusiasm into the home ranks.
Westerman missed a chance to reclaim the lead for Hull when he put a penalty attempt wide of the target but another probing run from Horne created the position from which prop Mickey Paea proved unstoppable from 10 metres out as he claimed his third try of the season.
Westerman was again off target with the goal attempt but Hull forced their visitors into a series of handling errors to keep them pinned inside their own half and Westerman clinched the win with a penalty and a drop-goal.
Hull FC: Shaul, Lineham, Whiting, Yeaman, Talanoa, Abdull, Horne, Paea, Houghton, Watts, Ellis, Hadley, Westerman. Substitutes: Green, Paleaaesina, Heremaia, Sa.
St Helens: Wellens, Makinson, Jones, Percival, Dawson, Wheeler, Turner, Amor, Roby, Walmsley, Flanagan, Manu, Soliola. Substitutes: Masoe, McCarthy-Scarsbrook, Laffranchi, Thompson.
Referee: Ben Thaler (RFL).