Salomon Rondon headed Tony Pulis' regimented and defensive-minded visitors into the early lead, but Claudio Yacob's mistake gifted Ritchie the late leveller.
Craig Gardner missed a first-half penalty for the Baggies, who were unable to hold out in a low-quality clash where Eddie Howe's Bournemouth ended their three-match losing streak.
The draw leaves both teams locked on 42 points with one game to play, with Bournemouth clearly the happier having secured their top-flight future in their maiden Premier League campaign.
Bournemouth's attack proved toothless for the majority, the hosts hogging possession but wasting almost all that superiority
West Brom's sole defensive error, in contrast, cost Pulis' men all three points.
Trademark Pulis defensive zeal from West Brom thwarted the limp hosts at every turn in a first half where the visitors ought to have turned around with a two-goal lead.
Bournemouth failed to pull apart West Brom's double-banked defensive lines to generate any sustained threat, despite dominating territory and possession.
Pulis' men were happy to let Bournemouth knock the ball about in front of them, lurking with intent to hit the hosts on the break.
And it paid off as they opened the scoring on the quarter-hour, Jonny Evans' neat cross allowing Rondon to hustle in front of the defensive cover to nod past Boruc.
Bournemouth's ineffective attacking forays continued for the brunt of the half, until Tommy Elphick's rustic challenge on Craig Dawson.
The Cherries defender had no arguments in conceding the penalty, but was to be offered a hefty reprieve from his goalkeeper.
Boruc palmed Craig Gardner's average strike onto the crossbar, and the West Brom midfielder was unable to connect cleanly under pressure from the rebound.
After the break the pattern of West Brom shutting the door on Bournemouth's attacking game continued unabridged.
Junior Stanislas wasted two half-chances with shots from distance, before replacement Callum Wilson dragged wide after racing into the box.
Rondon flashed a header wide in a rare West Brom foray, before Pulis threw Saido Berahino into the mix in a bid to drag his players slightly further up the field.
Berahino drew a smart low save from Boruc with his first meaningful touch, handing West Brom that necessary extra dimension.
Josh King blazed well wide on a break from the hosts, and then suddenly the Cherries were level.
Steve Cook's long throw drew an unforced error from Claudio Yacob, his unwitting flick gifting Ritchie the equaliser.
The replacement midfielder raced onto the loose ball and nodded past the stranded Foster to put the hosts on terms.
Ritchie's goal forced West Brom to chase the game and Dawson struck the base of a post from 20 yards, before Rondon just failed to latch onto Berahino's threatening ball in the box.