Passage through to the Second Round of the FA Cup was secured by the U's at Bromley, thanks to goals from Simon Hackney, Kayode Odejayi, Clive Platt and Steven Gillespie.
Bromley had soaked up a lot of pressure in the first half hour but couldn't stop Hackney and Odejayi give the U' a two goal half time lead and Platt and Gillespie added two more after the break.
A professional U's performance prevented any chances of an upset and the U's now look forward to the second round draw on Sunday afternoon.
The U's boss made three changes to his starting line, with two enforced due to the suspension of Anthony Wordsworth and the reluctance of West Ham to allow loanee Josh Payne to become cup-tied.
David Fox and Simon Hackney filled these places, while Phil Ifil took over on the right from Kevin Lisbie.
The pitch at Hayes Lane looked in great condition and the game started with no sign of the rain that was predicted to be sweeping in from the West Country.
The U's got into gear from the off and their first effort came on the third minute, when Phil Ifil had a cross deflected wide and Kayode Odejayi's header was cleared off the line.
Odejayi then hit his lob narrowly over the bar before Hackney volleyed wide and Clive Platt's header also flew wide.
Long range shots from Ifil and then Clive Platt failed to test the home keeper but Bromley were under the cosh against their league opponents.
And on the half hour, all the pressure bore fruit as two goals in the space of three minutes dampened any home hopes of an upset.
Simon Hackney latched onto a through ball from Odejayi and from the left edge of the box, rifled his left foot volley wide of Williams and into the top of the net.
Odejayi went from provider to scorer when he latched onto a long ball from the U's defence.
Platt was fouled but the referee played a great advantage and Odejayi used all his power and pace to evade two challenges before tucking the ball under the keeper to double the U's lead.
The visiting U's had the momentum and were going for more goals, with Ifil having another shot deflected wide.
Then just before half time, David Fox almost made it three but Williams in the Bromley goal superbly tipped the long range drive wide.
Aidy Boothroyd would have been happy that his side had converted the pressure into goals but would have reminded his players that the tie wasn't over and another professional forty five minutes was needed.
That's exactly what he got in what was a much quieter second period but the U's still found the net twice against the Blue Square South outfit.
It was Bromley who had the first chance though, as ex U's forward Gareth Williams struck a shot from an angle that Ben Williams had to get down well to save.
John-Joe O'Toole and Phil Ifil both failed to hit the target with efforts from outside the box before a long range shot from Erskine warmed Williams' hands with just over an hour gone.
On seventy minutes, any hope the home side had that they could get back into the game were dashed as Clive Platt scored with a header.
David Fox drifted a corner into the near post area and Platt was first to it and his downward header found the bottom corner.
Boothroyd made three changes as his side cruised through the final quarter of an hour and Steven Gillespie, Medy Elito and Joel Thomas were given the chance to impress.
O'Toole had a header acrobatically saved before Gillespie scored his first goal of the season, with Fox again the provider.
A patient build up led to Fox finding himself on the ball with Gillespie drifting behind his marker. Fox found him with a deft crossfield ball and Gillespie beat the keeper to the ball and headed home.
That fourth goal came just two minutes before time and the U's were good value for their victory and passage through to the Second Round.
U's: Williams, White, Okuonghae, Batth, Tierney, Ifil, Fox, O'Toole, Hackney (Elito), Platt (Thomas), Odejayi (Gillespie)