The Seagulls, starting with a 3-5-2 formation, had to defend heroically at times in the first half, with Ashton denied by two goal line clearances and a string of saves by keeper Chris Sanna, who had an excellent game.
The Bay then snatched the lead a minute before half-time when a long diagonal ball from Robbie Booth found Cory Williams on the left and his low drilled cross was turned into the net by Rob Hopley from close range.
They had a great chance to go 2-0 up in the second half when Chris Sharp broke free inside the area, but his shot was blocked by the keeper and Williams and Hopley both had shots blocked in the goalmouth as they tried to force the loose ball over the line.
Ashton made the most of that escape by going up the other end and equalising on 65 minutes through Dale Johnson’s close range deflection on a left wing cross.
The home side then pressed hard for a second but Sanna stayed strong and three headed chances for Ashton missed the target before a red card took the wind out of their sails.
Aaron Burns was sent off for going in with his foot as Sanna dropped on the ball with ten minutes left, and two minutes later Colwyn Bay won the game.
Following a free kick, Booth put over a great cross from the right and Fagbola scored the winner with a strong leaping header from 12 yards.
Manager Ash Hoskin said afterwards he was delighted to get the first away win, but admitted it had been a battle.
“Its not an easy place to come. Ashton play a brand of football that is hard to play against. The keeper is very direct to the big number ten and they have runners going off him so we had to stay disciplined.
“It was difficult to know what to do when it was 2-1, but we decided to put in a back four because even with ten men they were still bombing on, and its fantastic the way the lads have worked so hard, just 48 hours after the previous game, to get the three points.
“Michael Lea deserves a special mention because he has had to be patient and I thought he was magnificent. Chris Sharp ran his socks off and was very unlucky not to get a goal, and Chris Sanna had his best first half since the season started.
“I’m thrilled with the first away win, but of course it will mean nothing if we don’t follow it up with a home win over Frickley on Saturday – and the prepartion for that starts from now!”
Colwyn Bay: Sanna, Denson, Lea, Holsgrove, Fagbola, Love, Booth, Rodgers, Sharp (Zibaka 88 mins), Hopley, Williams (Dowling 73 mins). Subs not used: Corbett, Fernandes, Baynes.
More to follow