A try six seconds from the end of a pulsating Hull derby by debutant centre Jimmy Keinhorst earned Hull Kingston Rovers the spoils in front of a stadium record crowd of 12,100 at KCOM Craven Park.
Hull FC looked to have gained their first win for seven months when winger Bureta Faraimo went over for their third try 14 minutes from the end of a thrilling round one Betfred Super League clash.
But in the very last play, Hull KR worked the ball wide and Keinhorst - one of five close-season recruits - produced a spectacular dive at the corner that earned his side an 18-16 victory.
The visitors' pressure paid off with two tries in four minutes through Sika Manu and debutant Matty Dawson-Jones as Marc Sneyd kicked both conversions.
Rovers turned the tables in the second quarter. New captain Joel Tomkins slid over the line before Mitch Garbutt scored on his debut with Josh Drinkwater - another debutant - converted both tries before nudging his side in front with a penalty.
Keinhorst seals the win as Drinkwater misses the kick! pic.twitter.com/UGVQIHNM9V— Hull Kingston Rovers (@hullkrofficial) 1 February 2019
Hull hit back through Faraimo before Keinhorst decided it at the death.
Hull KR coach Tim Sheens said: “You don’t expect that with two minutes to go, being at your own end and really struggling, so to get down the other end without a penalty and come up with the right play was a tremendous effort.
“I was just about to replace Jimmy with Kane Linnett. He was struggling towards the back end because he hadn’t played a full game for quite a while but I thought he was good.
“Jimmy is the quiet achiever, nobody talks about Jimmy much, it’s always about everyone else.”
Hull coach Lee Radford said: “I walked into the changing rooms and they had their heads down so I told them to get their heads up. I’m proud of the performance.
The Black & Whites fell agonisingly short in their opening game of the Betfred Super League season as a late try from Jimmy Keinhorst claimed the points for @hullkrofficial at KCOM Craven Park.— Hull FC (@hullfcofficial) 1 February 2019
MATCH REPORT ➡️ https://t.co/mMCvEVQXlX pic.twitter.com/8sCCjtnCBu
"We did a lot of good stuff, unfortunately we just got nipped at the end. I thought we did enough to get a result. I thought in the first 20 minutes we looked really dominant but a couple of penalties let them off the hook.
“It just wasn’t to be but you’ve got to give them some credit. We were a bit clunky but we played with one half. I thought Washy (Danny Washbrook) did a great stand-in job."