West Brom made such a positive start and were in the ascendency early on, with Daniel Bachmann denying Grant from close range, but it was the visitors who took the lead in emphatic style.
As the clock hit the 11th minute, Sarr picked up the ball just inside his own half and, channelling his inner-David Beckham, pinged a pinpoint strike over the stranded David Button and into the net against the run of play.
Hornets manager Rob Edwards arguably boasts the best frontline in the division thanks to the exciting triumvirate of Emmanuel Dennis, Joao Pedro and Sarr, and it was Watford’s number 23 who displayed the kind of top-class talent which has seen so many elite clubs sniffing around the Senegalese star.
Eleven of Grant’s 18 goals last season came at home and just before the break, West Brom deservedly drew level.
Grady Diangana collected the ball in the middle of the pitch and with no pressure applied from the Watford midfield, the Congolese man curled a ball over the defence into the path of Grant, whose first touch and finish were that of a man brimming with confidence.
West Brom hadn’t beaten Watford since 2016, and that miserable run looked certain to continue after Conor Townsend inexplicably made a challenge in the middle of the park which inadvertently sent Sarr through on goal, leaving Semi Ajayi no option but to bring him down in the penalty area.
There was to be one final sting in the tail as Sarr, who had beaten Button from 50 yards in the first half, then failed to do so from 12, and with that poor spot-kick went Watford’s chances of snatching the win.
Steve Bruce, though, will be the more disappointed of the two managers - his side managed 19 shots to their opponents’ five on the night, but lacked a clinical edge to match their superiority.
Flashscore Man of the Match: Karlan Grant (West Brom)
