Liam O’Neil’s second-half goal saw League One Cambridge United beat Championship side Millwall to reach the second round of the Carabao Cup.

Millwall’s George Honeyman was sent off minutes later after being shown a second yellow card, leaving the Lions a man short for the final 30 minutes.

The man disadvantage cost Millwall as they crashed out of the competition.

Honeyman was given a second yellow card for a shirt pull on Saikou Janneh just after Cambridge had taken the lead.

It compounded Millwall’s predicament after Shilow Tracey’s ball from the right found O’Neil, who finished from from the top of the penalty area.

Isaac Olaofe squandered the Championship side’s best chance as he shot straight at Cambridge goalkeeper Will Mannion having been played clean through on goal.

Murray Wallace had earlier seen a curling shot cleared off the line for Millwall by Greg Taylor.

Olaofe’s header was then denied by the crossbar as Millwall pressed in six minutes of stoppage time.

Sam Smith failed to seal the tie as he fired over when one-on-one with Millwall goalkeeper George Long but the miss was not crucial as the U’s held on to progress.