New loan signing Omari Hutchinson created a second minute goal for Leif Davis but Saikou Janneh levelled for Cambridge United to leave the scoreline 1-1 at half-time.
Vaclav Hladky was in goal with youngster Ryan Carr, who signed from Carlisle in January, making his first start in the senior side at right-back, Leif Davis on the left and Luke Woolfenden and Cameron Burgess the centre-halves.
Lee Evans skippered in the centre of midfield alongside Massimo Luongo with Hutchinson on the right of the three behind striker Freddie Ladapo with Conor Chaplin and Marcus Harness alongside him.
League One Cambridge included on-loan Blues striker Gassan Ahadme, ex-Town men Paul Digby and Jack Lankester and one-time Playford Road academy schoolboy Ryan Bennett in their XI.
New boy Hutchinson was quickly into the action and in the second minute created a goal.
The on-loan Chelsea youngster exchanged passes on the right, worked himself space and then clipped over a cross for Davis, who scuffed a volley across home keeper Jack Stevens and into the corner of the net to give the Blues an early lead.
The game briefly boiled over soon afterwards following an overzealous challenge on Chaplin on halfway by Blues academy alumnus Bennett. Ladapo and others were involved in some pushing and shoving before order was restored by referee John Brooks.
Town, who had found the U’s difficult opponents when they were at the Abbey Stadium in League One in February when the game ended 1-1, continued to threaten, Chaplin seeing two shots blocked and then a third fly wide.
On nine, last season’s 29-goal top scorer swept the ball wide to Hutchinson, who curled a delicate effort just beyond Stevens’s top corner.
In the 13th minute, a swift one-touch move which started in the Town area ended with Davis whipping over a cross which was just beyond Ladapo and the ball was turned behind. Within a minute, Harness sent over another ball from the same flank but again just in front of the Town number nine.
Five minutes later, Cambridge struck their first shot of the game after the Blues had played themselves into trouble not far outside their area, however, Janneh scraped his shot wide.
On 24, Janneh got to the byline past Carr on the left and crossed but the ball scuffed off Ahadme’s head and away from goal.
That chance may have gone begging but five minutes later, the home side did get on terms.
Janneh, who had provided most of their threat, broke forward down the left and struck a shot from the edge of the area which deflected off Burgess, looped over Hladky and under the bar.
With Town’s performance having drifted since the equaliser, Cambridge fans thought their side had taken the lead in the 36th minute when Janneh planted a header past Hladky but having strayed offside.
Chaplin shot high and wide a minute later as the Blues sought to regain their earlier control.
But the half ended with Town still off the boil having made a blistering start via Davis’s Hutchinson-created goal and a number of other chances.
However, the U’s began to create opportunities and were worth their goal when it came even if the deflection was a little fortuitous.
Cambridge United: Stevens, Digby, Morrison, Bennett, Brophy, Thomas, Lankester, Dunk, Okedina, Janneh, Ahadme. Subs: Holden, Bennett, Andrew, Okenabirhie, Trialist, Sandiford, Simper, Yearn, McConnell, Hoddle.
Town: Hladky, Carr, Woolfenden, Burgess, Davis, Evans (c), Luongo, Hutchinson, Chaplin, Harness, Ladapo. Subs: Hayes, F Barbrook, Ayinde, H Barbrook. Referee: (Leicestershire).