Thomas out-paced Ben Tozer to race onto a long punt three minutes after the break before slipping the ball past Chris Dunn in the home goal.
That cancelled out a ninth minute header from Billy McKay, the home striker netting his seventh of the campaign from close-range after Andy Holt had stayed cool to chip a precise cross onto his head.
McKay almost made it 2-0 three minutes later but chipped over the crossbar as the home side dominated the first half as Holt saw a close-range drive cannon off Jeff Goulding before bouncing to safety.
Cheltenham almost levelled five minutes before the break but Ian Davis made a miraculous goal-line clearance from Ashley Eastham's header from a Danny Andrews corner.
After the Thomas equaliser the home side came close with McKay having one drive parried away by Scott Brown and seeing another glancing header just miss the target.
Source: PA
Source: PA