In a game of low quality, it was a deflected header which won it from a rare opportunity as Coulson met Ryan Ledson's cross and saw his effort bounce off Anthony Stewart and into the net.
Stewart later saw a header cleared off the line but there was no way through a stubborn United outfit and Wanderers will look to get back to winning ways at Newport County on Saturday.
Gareth Ainsworth made just the one change to his starting line-up from the side that won 1-0 against Bristol Rovers on Saturday, with Sam Wood replacing the injured Marcus Bean.
The first sight of goal fell to the hosts when Ryan Ledson’s speculative cross-shot curled over the bar in the wind, before the creator and scorer of Saturday’s winning goal combined again when Joe Jacobson delivered a free-kick into a dangerous area, but Luke O’Nien couldn’t divert his header away from the keeper this time around.
Jimmy Spencer then headed an inviting cross from Harrison Dunk over the bar after the United winger sped away down the left, and Spencer then sent a half-volley just wide of the post with an exquisite effort from the corner of the box.
Wanderers’ best opening arrived midway through the half when Luke O’Nien fed Matt Bloomfield in the box with a clever reverse pass, and his low cross was glanced on by Max Kretzschmar but not with enough contact to send it goalwards.
But the deadlock was broken at the end when Ryan Ledson’s cross from the left-hand corner of the box was met by the head of Josh Coulson, and his effort took a significant deflection to wrong-foot Ryan Allsop and find the back of the net on 28 minutes.
There were no further chances as the half ended scrappily, although Wanderers had found a way of nullifying the threat down the left by reverting to a flat midfield four.
They showed signs of improvement early on after the break, with Matt Bloomfield just unable to reach Sam Wood’s drilled cross, before Max Kretzschmar’s free-kick was deflected wide by the wall after Luke O’Nien was tripped 20 yards out.
However, home keeper Will Norris remained untested and Gareth Ainsworth turned to the bench to bring top scorer Garry Thompson into the mix, lining up alongside Paul Hayes in attack at the expense of Max Kretzschmar.
The Blues attempted to retain the ball higher up the pitch but struggled to find the killer ball inside United’s box, while Harrison Dunk did find room to shoot from a tight angle at the other end but it was comfortable for Allsop to save at his near post.
Home keeper Norris looked nervy under pressure and Wycombe looked to capitalise, almost forcing an equaliser when Anthony Stewart’s looping header was cleared off the line by Leon Legge before Norris dropped Sam Wood’s cross only for it to be scrambled clear.
United adopted the ‘anywhere will do’ approach to protect their lead but struggled to hold the ball up front, giving the Blues hope of working their way back into the game if they could penetrate an effective backline.
One last throw of the dice saw Ryan Sellers brought into the game in place of Sam Wood, but the four minutes of stoppage time never looked like yielding a goal at either end as the Blues rued the missed opportunity to build on their superb weekend win.
Wycombe: Allsop, Harriman, Jacobson, Stewart, McCarthy, McGinn, Bloomfield (Ugwu 76), Wood (Sellers 87), O’Nien, Kretzschmar (Thompson 56), Hayes.
Unused subs: Richardson, Jombati.
Cambridge: Norris, Furlong, Haynes, Legge, Coulson, Ledson (O’Neill 78), Berry, Dunne, Dunk (Donaldson 87), Spencer (Simpson 68), Williamson.
Unused subs: Beasant, Omozusi, Keane, Roberts.
Referee: Mr Simon Hooper
Attendance: 4,141 (325 from Wycombe)