The Coatbridge side were on course for all three points after David Crawford gave the visitors the lead at Stair Park, writes Chris Jack.
They were soon left disappointed though as Craig Malcolm converted from the spot with just seconds to go to seal a dramatic equaliser.
The late drama meant Rovers missed a chance to move five points clear of their relegation rivals at the foot of the Irn-Bru Second Division.
Lumsden, who handed debuts to Partick Thistle duo Christie Elliot and Bradley Halsman hours after securing them on loan, admits his side's failure to add to their lead while on top was crucial.
He said: "The game should have been done and dusted as we had some really good chances to score.
"If you don't take your chances you always run the risk of being punished, as has proved to be the case."