Lancaster City failed to press home a dream start and slumped to a third consecutive defeat in front of almost 3,000 people.
Mark Jackson gave City a shock lead after just two minutes and shortly after the hosts equalised, Aaron Helliwell made it 2-1 with a composed finish.
But FC United of Manchester immediately hit back and ran out clear winners in the end.
City striker Jackson stunned the home crowd after just two minutes when he raced clear beyond the last defender and tucked the ball into the bottom corner.
However, FC United responded well and punished some sloppy City defending on 14 minutes.
The unmarked Stuart Rudd chested down a lofted pass and dinked the ball over an advancing Ben Price - again deputising for the injured Mark Thornley - from close range.
To their credit, City continued to look dangerous and unexpectedly restored their lead.
Midfielder Helliwell made room for himself in a congested penalty area and arrowed a left-footed shot into the far corner.
But on this occasion City's lead lasted less than two minutes as FC United scored the game's fourth goal after just 20 minutes, home midfielder Rob Nugent heading home a corner.
Both sides continued to surge forward at a frantic pace and Craig Redhead saw an effort parried away by Ashton.
But a dreadful mistake from shot-stopper Price swung the match in FC United's favour. On 28 minutes, the youngster failed to hold onto Rory Patterson's harmless long-range effort and the ball trickled into the net.
However, City ended the half on a high as Jackson struck a venomous effort against the bar, while Mike Rushton and Tom Entwisle also came close to scoring.
Meanwhile, goalkeeper Price suffered a nasty blow to the face after spilling a shot which a home forward looked to retrieve in a 50-50 challenge.
The visitors started brightly after the interval and should have equalised. Helliwell was denied by the feet of Ashton, while Rushton fired an effort inches wide.
But City paid the price for not converting their chances as top-scorer Patterson completed a brace with a neat close-range finish on 54 minutes.
Nugent grabbed his second and FC United's fifth with 20 minutes left when he powerfully headed home another corner.
City continued to pose a threat in the closing stages as Rushton was thwarted at point-blank range, while the excellent Jackson thumped a free-kick against the bar.
At the other end, Price atoned for his earlier blunder by making three superb saves in the last 10 minutes.
Lancaster City: Price, Uberschar, Redhead, Heffernan, Swan, Stringfellow, Rushton (Rigby 77), Entwisle, Love (Jeffrey 65), Jackson, Helliwell.
Referee: M. J Denton.Attendance: 2,704.
Last Updated: 15 April 2008 12:18 PM