A point apiece means West Brom stay in the play-off spots overnight – edging up to third in the table – with the hosts keeping themselves out of the drop zone with a move up to 17th.
Neither team created much in a timid opening at both ends of the pitch as Adam Reach lashed a long-range strike well over the top for West Brom before Patrick Bauer flicked a header wide from a deep corner.
The Baggies did look set to increase the tempo before the break, however, as the busy Grady Diangana forced a diving stop from Daniel Iversen before Preston pounced to edge themselves in front on 27 minutes.
Daniel Johnson’s firm tackle in midfield bounced kindly for Emil Riis and when his flick freed Ben Whiteman on the edge of the box, the former Sheffield United man’s deflected strike flew straight past England international Sam Johnstone.
But despite that setback the visitors showed their promotion-chasing class just before the break, as Scotland star Matty Phillips produced a deserved equaliser.
Darnell Furlong’s long throw-in caused major panic inside the Preston box and Phillips stooped down – amid the penalty area pinball – to bravely nod past Iversen in added time.
The visitors pushed hard to build on that immediately after the restart, as Phillips stepped away from two tackles to curl an effort over and Diangana forced Iversen to claw out his cross-shot just before the hour mark.
Both managers did look to try and force the issue in the closing stages with attacking changes, with Karlan Grant and Callum Robinson replacing Diangana and Phillips and the fit again Connor Wickham coming on for Sean Maguire.
West Brom continued to boss possession in the final 20 minutes but it was McAvoy’s Preston who carved out the strongest chance to snatch all three points late on.
Some loose possession from the Baggies was seized upon by Preston on the break but Ryan Ledson’s driven effort was acrobatically kept out by Johnstone.
That miss was almost punished by Ismael’s visitors in the 90th minute but when Grant slipped in Jordan Hugill inside the box, Iversen was quick off his line to make a brave block and deny the Norwich loanee a late goal against his former club.