Viktor Gyokeres' stoppage-time penalty halted West Brom's five-match winning run as the Baggies lost 1-0 at Coventry.
The run, that included four clean sheets, had taken Carlos Coberan's team from the foot of the Championship to within touching distance of the top half.
But in a game destined for a goalless draw despite numerous chances for either side, Gyokeres twisted and turned his way into the box and was brought down by Erik Pieters.
Coventry's top scorer dusted himself down to step up and send Alex Palmer the wrong way, securing the Sky Blues' first victory since the international break.
Earlier, Jonathan Panzo almost netted the winner after he opened the scoring in Saturday's enthralling 3-3 draw against Swansea, in which the Sky Blues surrendered a three-goal lead.
The on-loan defender rose highest from a Gustavo Hamer corner, but his header rattled the top of the crossbar and went behind.
At the other end, Darnell Furlong saw his close-range header saved well by Ben Wilson from John Swift's deep free-kick.
Former Salford striker Brandon Thomas-Asante was the only change to either starting line-up ahead of kick-off as he replaced Daryl Dike in the Albion XI.
Callum O'Hare had the first chance of the evening inside six minutes after Gyokeres' persistence down the left but the former Aston Villa midfielder steered his effort wide from inside the box.
Gyokeres also tried his luck to open the scoring in the first half, firing wide after Hamer's layoff.
Some superb defensive work from Callum Doyle stopped Albion from getting their noses in front, first preventing Thomas-Asante's cross from reaching Jed Wallace. The Manchester City loanee was then up quickly to clear Tom Rogic's effort off the line following Jake Bidwell's missed interception.
Hamer's superb ball set Gyokeres free down the right, but his effort was straight at Baggies goalkeeper Palmer.
From the resulting corner, Wallace found himself bearing down on Wilson's goal and should have done better with his tame effort that was comfortable for the Sky Blues 'keeper.
Matt Phillips also set his sights on the game's first goal after Connor Townsend's cross found its way to the winger on the far side of the box, but he could only blaze his effort over.
But Gyokeres was to have the final say, converting his penalty to notch an 11th Championship goal of the season and secure Coventry a first home league win over Albion since 2003.
What the managers said...
Coventry's Mark Robins: "There was no doubt in my mind he was going to bury that and thankfully he did and we've come away with three brilliant points. If you look at what happened I think (West Brom's Dara) O'Shea started to scuff the penalty spot up which he got the yellow card for, they try and slow things down, whether it's right or wrong I don't know, that's for their manager to sort out.
"Ultimately, they're trying to win a game of football however they can and it took a little bit of time so there's a bit of thinking time for him, but one thing I know about Vik is that he'll just be calm and he was."
West Brom's Carlos Corberan: "It was a very tough game. We were suffering a lot in the first 30 minutes, they were better than us in attack, they were better than us in defence, we couldn't stop them and in our stuttering attack we couldn't dominate them.
"In the last 15 minutes of the first half we started to control the positional attack, we started to attack more, we started to attack better and the team started to take a little bit more control of the game. In the second half we didn't suffer, I don't remember any big actions in defence in the second half, but it's true in attack we couldn't create enough chances to unbalance the game."