Millwall reached the Carabao Cup third round for just the second time since 2011 after Matt Smith rounded off a comfortable 3-1 victory over Cheltenham.

The striker tapped home on the hour to wrap up the contest and set up a tie with either Burnley or Sheffield United, to be played at The Den next week.

Ryan Leonard fired home superbly to give the hosts an early lead, with Connor Mahoney capping off a fine performance with the Lions' second just after the break.

Half-time substitute Finn Azaz got one back 20 minutes from time but it wasn't enough for the Robins to reach the third round for the first time in their history.

Cheltenham started positively though a major goal threat was lacking, with Will Boyle only able to head Ben Tozer's long throw straight at Bartosz Bialkowski.

Millwall quickly settled and became the stronger side, Smith heading narrowly wide against his former club while Mahoney forced a low stop from Josh Griffiths.

And the breakthrough came just 20 minutes in with Smith nodding a cross into the path of strike partner Tom Bradshaw, who in turn teed up Leonard for a sumptuous 20-yard strike.

The hosts remained dominant with Ryan Woods nodding wide while Leonard threatened a second long-range strike, though this one flew harmlessly wayward.

The Robins still posed a threat, however, with Alfie May looking the most likely though his 25-yard shot drifted wide late in the first half.

May was in Millwall's academy until the age of 14 and had the ball in the net against his former side, with the last chance of the first half ruled out for offside.

The visitors had shown promise but it took just three minutes of the second half for the Championship side to double their lead.

Shane Ferguson found space down the left, crossing for Mahoney to hammer in a goal his performance deserved.

That setback sparked the Robins into life, with Azaz having an effort well blocked a few minutes after coming on.

But the game was put to bed when Ferguson got himself on the end of a deep right-wing cross, nodding back in for Smith to tap home just after the hour.

To their credit, Cheltenham kept fighting and threatened a comeback when Azaz's wicked strike from outside the area proved too much for Bialkowski to handle.

The 20-year-old was not done there, twisting and turning on the edge of the area before forcing the Millwall keeper into a smart stop.

But his first senior goal proved just a consolation as Cheltenham's bid for Carabao Cup club history came unstuck in south London.