West Brom entered the fixture winless in their last four after a strong start to the season, but would be hoping to pick up the points against a club that would likely be competing with them for league position come May.
Watford had an outstanding away record moving into the clash, and would be sixth when the first whistle blew. Victories over Bournemouth, Southampton and Swansea on the road had raised their confidence.
Jonny Evans was started at centre back for the Baggies in a 4-2-3-1 formation with Jay Rodriguez used as an attacking midfielder behind Salomon Rondon. Watford were unchanged from their 2-1 win in Wales except for the replacement of Andre Gray with Troy Deeney.
Watford began the match positively, keeping possession well without creating much of note. The Baggies were promising on the break though, and Matt Phillips was unlucky not to be joined by attacking numbers on the edge of the Hornet's 18-yard box.
Moments later, however, and the home side had taken the lead. Watford's back four have impressive physicality, but Christian Kabasele was too easily shrugged off the ball when Salomon Rondon outcompeted him off a long ball. He then worked a shot in off a close angle.
A shell-shocked Watford found themselves two down just three minutes later, this time off a corner as Jonny Evans powered home with Ahmed Hegazi also arriving. The Egyptian then missed a header of his own after Heurelho Gomes flapped and missed.
Watford settled down a little and began to pass with more incision. A one-two between Richardson and Deeney allowed the former to cross for Andre Carrillo, but the header rose over the bar practically from an open goal.
Never mind, for the goalscoring action continued and this time it was the visitors who bagged. Abdoulaye Doucoure took the credits as he was supplied by Richardson down the left. Doucoure then drove towards goal and fired home, via a touch from Jonny Evans, into the bottom corner.
The Baggies rode their lead into the second half, which started as slowly as the first. Ten minutes in, an Etienne Capoue strike from twenty-five yards was goal bound had it not deflected off the evergreen Gareth Barry.
The Hornets brought Roberto Pereyra on for Capoue as they aimed for attacking creativity to level the scores, while West Brom replaced Chris Brunt with Jake Livermore.
A Ben Foster gaffe allowed his former club an opportunity from a corner, and they might have taken it as Kabasele missed a diving header - and the chance to leave the keeper red-faced. The pressure continued to build as Richarlison headed wide moments later.
The introduction of Andre Gray for Carrillo showed Marco Silva's determination to salvage an equaliser with two strikers on the pitch. It was not helpful for the away side when Richarlison collapsed holding his back and recovered only a couple of minutes later.
The minutes ticked by though, and soon Watford had only stoppage time to save themselves a point. Nail-biting moments awaited for West Brom as the Hornets applied late pressure - and in an incredible twist at the death, they equalised through a Richarlison header!
A late cross was swung into the area with most of the Watford side piling in for it, and Richarlison was the one to leave the net bulging. Marco Silva might still have felt, when the final whistle blew after the kick-off, that they ought to have taken all three points despite the excellent comeback.