Both goals in the match came under repeated fire and the keepers pulled off some fine saves in a hard-fought encounter in which a draw was a fair result.
United manager Paul Simpson said: "We deserved something out of the game.
"We showed a lot of character in the second half and we definitely earned a draw."
However, he was "very suspicious" of Scarborough's controversial goal which
came in the 37th minute through Mark Hotte from a Neil Redfearn corner.
United's Peter Murphy struggled to stop it going over the line but referee David Richardson ruled that it had crossed.
The resulting protests from the Cumbrians resulted in Simon Grand being booked for dissent.
Scarborough manager Nick Henry said: "It was a fantastic game. We had the
best chances in the first half but Carlisle came back strong after the break.
"It was a fair result in the end."
He reserved special praise for David Reeves - the 37-year-old former Bolton, Carlisle, Preston and Chesterfield forward who signed for the Seadogs three days ago.
"He defended well and his fitness was terrific," said Henry.
Scarborough, still unbeaten at home this season, produced one of their best
performances before their second biggest crowd of the campaign.
But it was United who had the best of the chances in the early stages thanks to Andy Preece, Chris Billy, and Lumsdon who each went close.
Scarborough's Steve Baker and Chris Senior hit back and they were unlucky not to go ahead when Senior drove a great ball just inches wide from 15 yards.
Then five minutes later keeper Matt Glennon only saved a speculative header from Senior at the second attempt.
The second half became more tense after Scarborough had taken the lead with United throwing everything up front.
Glenn Murray had a fine chance to equalise but mis-judged a back flick then had another effort brilliantly saved by Leigh Walker.
There were further chances at both ends before United found the equaliser with three minutes to go when Preece flicked on a free-kick and Lumsdon finished off the move by putting the ball low into the net.