Both have been forced to self-isolate after being deemed close contacts of three Scotland Under-21 team-mates who have tested positive for Covid-19 since returning from Greece in midweek.
The Steelmen brushed off the late blow and took the lead in the 17th minute following a strong opening.
But the ball broke kindly for O'Hara and the midfielder drilled in from 12 yards out.
The midfielder was eventually taken off the pitch on a stretcher to be replaced by Craig Bryson.
But shortly after the restart Saints drew level.
A move saw them burrow their way into the area and Bevis Mugabi was tempted into a rash challenge that upended May.
The striker picked himself up to drill in his third penalty in two games.
Wotherspoon and O'Hara went close with headers at either end before the half concluded with a chance for the visitors.
Cole received the ball with his back to goal and swivelled swiftly to despatch a low shot but Zander Clark got down smartly to block.
The second half was nip and tuck as both sides probed tentatively for openings.
But defences held the upper hand to keep both sets of attackers at bay.
Saints did feel aggrieved when Craig Conway was caught late by Mugabi after heading goalwards, with the winger subsequently having to be substituted with a facial injury.
Another header brought the home side's next opportunity 19 minutes from time. Wotherspoon's corner was headed down by Kerr and helped on by May but Motherwell keeper Aaron Chapman held firm on the line.
When substitute Chris Kane blazed over from a tight angle any prospects of a late winner slipped away.