Rovers were beaten at Charlton Athletic after failing to turn possession into an equalising goal.
Tariqe Fosu’s early strike made the difference, with the Addicks man striking after collecting the ball from Jay Dasilva.
Rovers were unchanged from the previous Saturday’s win over Southend United, with Rodney Kongolo and Marko Marosi returning to the bench after international duty and injury respectively.
The game started in patchwork manner, with a lot of stoppages. John Marquis required treatment after a cut to his forehead, and James Coppinger had to come off after just seven minutes due to a calf injury.
Kongolo came on in his place, taking up a position on the right of midfield with Ben Whiteman pushed to the tip of the diamond to fulfil the role vacated by the departed Rovers captain.
It got worse two minutes later when the Addicks scored the only goal of the game, with Fosu striking with a powerful shot at the neat post.
Rovers patiently played themselves back into the game, enjoying plenty of possession though neither keeper were under real pressure until the 25th minute when Alfie May was left with too much space on the edge of the area and clipped the ball off the top off the bar with a dipping effort.
Lawlor kept the score at 1-0 as he palmed away Ricky Holmes’ free-kick, then kept out Josh Magennis’ header.
Home keeper Danny Amos had to be alert to keep out a Tommy Rowe header, then a low Harry Toffolo free-kick.
The home side were the last to threaten in the opening period, with Lawlor denying Holmes before goalscorer Fosu was booked for simulation in the follow-up.
There were no changes at the interval, and the start to the second half was held up in bizarre fashion.
Rowe took the kick-off for Rovers, but as the ball was being played upfield Magennis clattered into referee Robert Lewis - the collision was entirely accidental, but the forward took out the official with a shoulder to the face.
Lewis was knocked out cold by the incident, though he was able to walk off after a delay of around seven minutes. Fourth official Craig Hicks had to step in and, with 52 minutes on the clock, Rowe kicked off the second period again.
Rovers created plenty of chances, with John Marquis firing a half-volley over after Toffolo’s delivery from the left.
As the game became stretched, only a combination of determined defending - Lawlor pulled off a great save, while Joe Wright headed an effort onto the bar - and the woodwork kept Billy Clarke and Magennis out from a goalmouth scramble just after the hour mark.
Rovers were forced into a change for the second time in the match shortly afterwards, with Alfie May coming off due to injury an Liam Mandeville coming on in his place.
Lawlor got down well again to keep out a deflected Fosu shot which came off Wright, doing the same to palm away a Magennis shot and an Ahmed Kashi effort .
Rovers created the best of the final chances, with Chris Solly getting up well to force Rowe’s good header from the left behind for a corner.