The centre-forward cancelled out Nicky Forster's early spot-kick for the home side to give Rovers a deserved share of the spoils.
Brighton boss Micky Adams was forced into two changes to the team which had beaten Crewe and Barnet in impressive fashion.
Gary Hart, released by former manager Dean Wilkins at the end of last season and then re-signed by Adams, took over from the suspended Glenn Murray up front and summer signing David Livermore made his full debut with Kevin McLeod injured.
The alterations did not look like unsettling Brighton initially. Forster forced keeper Steve Phillips into an early save before putting Brighton in front in the tenth minute.
The skipper's shirt was tugged by David Pipe as he tried to latch onto a cross from Dean Cox.
Forster made no mistake with the penalty, raising his tally to three goals in as many games. The rest of the first half was untidy and uneventful but Rovers fought back after the break.
Lambert almost equalised three minutes into the restart with a free-kick from 20 yards over the defensive wall which hit the crossbar.
Steve Elliott also volleyed wide from Stewart Campbell's corner for the visitors as Brighton laboured to hold onto their lead.
Goalkeeper Michels Kuipers, playing against his old club, looked as if he had preserved victory for Brighton in the 76th minute when he touched Lambert's snap-shot from a lay-off by substitute Ben Hunt onto the post.
Lambert, having hit the woodwork twice, finally made amends with four minutes left. Craig Disley had his shirt tugged as Kuipers blocked his close-range shot and Lambert confidently despatched the resulting penalty.