This should have been another.
Instead, his crisply-hit 73rd minute strike in front of the North Stand was the precursor to more Albion disappointment as they drew 1-1 with Everton.
And this was as biting as any of that disappointment they have endured in a run which now extends to one Premier League win in 11 games.
A strike by Beto in the seventh and last added minute gave Everton a draw and brought boos around the Amex.
It was a sickening disappointment for home fans and players, some of whom collapsed to the ground at full-time.
They failed to see out the closing stages and paid the price when Bart Verbruggen could only parry a low shot after a cross was allowed to come in.
What should have been the relief of a win will just lead to eight days of angst and finger-pointing before Crystal Palace visit next Sunday.
Albion had just taken off Gross before that goal, replacing him with James Milner.
The ploy of bringing on Milner to see wins out just does not work, although a stray pass by Carlos Baleba plus some poor marking were more relevant here.
So the glorious Gross story was kept on hold.
The German scored Albion’s first two goals in the Premier League and a famous winner at home to Manchester United.
Then there was the first at Marseille to help them a first Europa point.
Two on the opening day at Old Trafford.
This one felt more like one of his forgotten precious strikes.
That came just before Christmas, 2017, to secure a 1-0 win over Watford during the club’s first tough run in the Prem. A bit like the one they are on now.
His breakthrough this time was expertly crafted and finished.
Yasin Ayari pulled the ball across the face of goal from the right edge of the box.
There was a brilliant dummy from Charalampos Kostoulas to allow the ball to run.
And Gross sent it home with a clean connection on the right foot, finding the bottom corenr.
It was his first goal since returning to the club and the celebration in front of the North Stand showed what it meant to him.
It looked like it would mean a lot to his club until those fateful last seconds.
After one win in ten leagues games, there was unease in the air which should have been lifted in the first half.
Kaoru Mitoma guided a shot just past the far post after a superb link-up with Danny Welbeck.
And Welbeck soared but headed wide amid the Everton giants at a corner.
There was also a sharp save by Jordan Pickford from Welbeck’s clever back heel.
But Everton were more of a threat in the second period and Verbruggen used his left foot to make a key save from Kiernan Dewsbury-Hall.
The same Everton man had earlier whipped a shot narrowly past the far post.
And it looked like it was Jake O’Brien, whose long throws posed a threat, who managed to divert a Michael Keane header away from the Albion goal.
Then Gross struck. And that should have been the game's main storyline.