After snatching the lead through Michael McGlinchey's well-taken eighth-minute strike - marking the midfielder's 150th A-League match as one to remember against his former club - the Phoenix appeared content to let the home side dictate terms.
They visitors were largely living on scraps and, with heavy rain falling throughout the first half, unable to effect their usual brand of possession football.
Central Coast immediately enjoyed ascendancy after falling behind but their continual crosses and succession of long-range shots lacked the requisite quality to seriously threaten Glen Moss' goal, with the goalkeeper rarely required to intervene.
But too often the Phoenix were inaccurate when they won the ball, managing to hold their slender lead heading into halftime only after being forced to do plenty of dirty work around their own area.
The attack continued to struggle for fluidity in the second spell, with periods of possession repeatedly breaking down in the middle third, leaving Andrew Durante and Ben Sigmund to lead an obdurate defence that continued to repel most of the Mariners' own raids.
Frustrated by their inefficiency, the home side begun committing plenty of numbers forward as the match progressed, giving the Phoenix a few tempting opportunities on the counter. While one such move saw a fierce Roly Bonevacia drive denied by a combination of Paul Izzo's fingertips and the outside of the post, too many were squandered.
Still, with Central Coast failing to find either a suitable final pass or a precise finish, the Phoenix would have been hopeful of walking away with all three points. The mounting pressure was creating a test relished by central defenders and Durante and Sigmund were throwing their bodies in front of shots and putting their heads in where it hurts.
But all their commitment was eventually undone when O'Donovan pounced, with the Irish striker producing a fine header from Josh Rose's corner to provide his side with the equaliser their enterprise deserved.
Central Coast Mariners 1 (O'Donovan 76)
Wellington Phoenix 1 (McGlinchey 8)
HT: 0-1