Full-time score from The Den
It proved to be a bittersweet night for debutant Mattthew Briggs, who scored the 27th-minute winner, was booked for taking his shirt off to celebrate and then shown a second yellow card for a tackle with 58 minutes on the clock.
Millwall's 10 men battled their way through to the Second Round of the Capital One Cup with a narrow victory against Wycombe Wanderers at The Den.
Briggs, Magaye Gueye, Byron Webster and Lee Gregory all came into the team, whilst the subs bench consisted of six Academy graduates - Fred Onyedinma, Josh Siafa, Aiden O'Brien, Jack Powell, Jake Goodman and John Marquis - plus goalkeeper Stephen Bywater.
Briggs was one of four summer signings to make their first starts for The Lions as manager Holloway made seven changes in all from the team that started against Leeds United on Saturday.
Although the official attendance was around one fifth of the 16,000 that packed The Den on Saturday, credit to those who did turn out to support the boys in blue as The Lions extended their unbeaten run in League and Cup competitions to 10 games.
However it was not all plain sailing for the home side who were pushed all the way by a determined Wycombe side who, in the first half, shaded possession and chances, but found themselves trailing by Briggs' goal at the break.
It took a stunning save from Lions keeper David Forde to acrobatically tip Paul Hayes thunderous volley away on seven minutes and then Paris Cowan-Hall headed wide of the mark as Wycombe threatened once more.
The home side produced their best chance of the opening exchanges just before the quarter-hour mark when a delightful slide-rule pass from Gueye picked out Gregory, but the latter just couldn't get the ball under control and keeper Matt Ingram raced off his line to collect.
There was a slight defensive reshuffle made soon after with skipper Alan Dunne moving to centre half alongside Danny Shittu in a straight swap that saw Webster slot in at right-back.
Wycombe kept plugging away in the torrential rain trying to find a way through, and it took another smart stop from Forde to deny Sido Jombati an equaliser seven minutes before the break, diving low to his right to push the full-back's stinging shot away for a corner.
That proved to be the visitor's best chance of the half and it was Millwall who went in one goal to the good.
Midfielder Powell entered the fray for his senior debut on 63 minutes, replacing McDonald as the 10 men of Millwall regrouped and it was infact The Lions who looked the more likely to score again, despite their numerical disadvantage.
Booking: Cowan-Hall (88mins)