Millwall defeated Barnsley 1-0 in the Sky Bet Championship at Oakwell on Saturday afternoon.
Murray Wallace's header a minute from time gave The Lions a second consecutive single-goal victory and a first away success of the campaign.
Gary Rowett made two changes from the side which defeated Bristol City 1-0 on Wednesday night - one enforced - as Jake Cooper and Jed Wallace returned to the side at the expense of the injured Scott Malone and Matt Smith.
On a rainy day in Yorkshire, the first opportunity went the way of the hosts as early as the second minute, but Bartosz Bialkowski was able to tip Aaron Leya Iseka's attempt wide.
Two minutes later, The Lions worked themselves into a good position with Sheyi Ojo cutting in on the left-hand side and striking towards goal - his initial effort was blocked, with Murray Wallace's close-range follow-up being deflected behind.
Millwall then had to sit back as Barnsley came on strong, with Jasper Moon and Ben Williams trying their luck, whilst at the other end, George Evans' curler went just wide of the post in a start of full of chances for both teams.
With 19 minutes on the clock, Bialkowski had to be on guard as Shaun Hutchinson uncharacteristically lost possession to Devante Cole and allowed the striker a run on goal, but the Pole was there to smother his shot and keep the score goalless.
Murray Wallace had a second attempt at Brad Collins shortly after but found his attempt tipped over, with the lively Leya Iseka proving troublesome for The Lions in beating Jake Cooper before striking on 29 minutes, but it skipped wide of the post.
Millwall were getting into good positions as the half wore on, most notably down the left-hand side, but were just unable to get that final shot away - Benik Afobe battling well after controlling inside the penalty area, but The Tykes were able to scramble his shot away off the wet surface.
The ball was making its way into the Barnsley penalty area more so than the other way round as half-time approached, with crosses from Jed Wallace and Afobe entering the box, but a combination of a solid Tykes defence and a lack of killer instinct meant Brad Collins remained largely untested. A delightful cross from Murray Wallace almost found the run of Afobe with just over five minutes to play, but the ball skipped off the turf and out for a goal-kick.
Murray headed over his namesake Jed's corner-kick shortly into the second-half, before Jed raced away on goal and looked to shoot after springing the offside trap and finding himself in the area, but a superb tackle from Liam Kitching kept Barnsley's sheet clean.
George Saville hooked Jed Wallace's lofted pass towards goal as the hour-mark came into view with The Lions controlling the game, but George Evans directed his header away from goal on the follow-up.
Rowett opted to bring on Billy Mitchell and ex-Barnsley man Tom Bradshaw with 20 minutes remaining, and the latter was in the action five minutes later as he flicked Jed Wallace's cross towards goal, but it was a comfortable one for Collins to stop. Bradshaw then broke through the defence and forced a save from the goalkeeper, with a goal-bound header from the resulting corner-kick also stopped by Collins.
Barnsley substitute Dominik Frieser then headed into the side-netting with eight minutes left to play, before Jed Wallace blazed over at the other end with time ticking away. Callum Britain then incensed the Oakwell crowd by slicing well wide as The Tykes mustered a rare attack, but with a minute to play, The Lions finally got the reward their dominance had deserved as Murray Wallace powered home a Jed Wallace corner to open the scoring.
Billy Mitchell dragged a shot wide in four minutes of injury-time, but The Lions were able to see the game out and claim three deserved points.
Barnsley: Collins, B. Williams, Styles, Kitching, Brittain, Woodrow, Leya Iseka (Frieser 70'), Moon, Palmer (Sibbick 55'), Helik, Cole (Adeboyejo 67'). Subs not used: Walton, J. Williams, Gomes, Oduor.
Booking: Palmer, Adeboyejo
Millwall: Bialkowski, McNamara, M. Wallace, Hutchinson, Cooper, J. Wallace, Ojo (Bradshaw 69'), Saville, Afobe (Smith 76'), Ballard, Evans (B. Mitchell 70'). Subs not used: Long, Kieftenbeld, Pearce, Leonard.
Scorer: M. Wallace 89'
Referee: David Webb
Attendance: 11,888 (511)