Ryan Babel opened the scoring for the Cottagers three minutes into the tie before Chicharito drew the Hammers levelled.
Diop then handed Manuel Pellegrini’s men the lead in the 40th minute, heading home Robert Snodgrass’ cross and Michail Antonio sealed the victory in additional time.
Impressed by the win and his maiden goal in the English top-flight, the21-year-old has taken to the social media to celebrate the feat.
“Victory, very happy to score my first goal in the Premier League tonight and help the team to win this derby,” Diop posted on Instagram.
The victory saw the Hammers move to the ninth spot in the log after gathering 36 points from 27 games.
Diop has made 30 appearances for West Ham United since joining the side from Toulouse last summer, helping them to keep six clean sheets and scoring twice.
The defender will look forward to another impressive showing when West Ham visit Manchester City on February 27.