Yannick Bolasie beat his full-back before crossing to Damien Delaney, whose header was saved well by Robert Olejnik. Murray pounced on the rebound, but it was deflected just over the bar.
Bolasie was Palace's main creative force in the first half and another cross from the winger fell to top scorer Murray, but the striker somehow contrived to head over from four yards out.
Peterborough continued to carve out chances, as a good effort from Mendez-Laing fizzed just wide.
Just before the half-hour mark, Tomlin gave Posh the lead with a good goal. The centre-forward took on three defenders before firing a low shot into the corner.
Peterborough continued to attack in search of a second goal and minutes after being booked, Delaney gave the ball away to Nathaniel Mendez-Laing and his cross just evaded Tomlin and Gayle.
But Palace got back into the game on the stroke of half time, when Gabbidon was brought down in the box following Garvan's corner. Murray stepped up to level the scores and notch his 30th goal of the season.