Thornton kept up the heat on the top four with victories against Andy Hamilton and Adrian Lewis at the NIA.
“It was an important couple of wins for me,” admitted the Scotsman, who faces Phil Taylor next week in Liverpool.
“I have slipped up a bit in the last couple of weeks but I’ve kept myself in it and I’m looking forward to the challenge of reaching the play-offs.
“I’ve had the better of Phil in our last few matches so if that continues then I’ve got a great chance of closing the gap.”
Whitlock was denied a double when he lost out to Taylor after seeing off league leader van Gerwen earlier in the evening.
Raymond van Barneveld came out on top in his match against James Wade, while Lewis lost to Taylor in the other match of the night.
By Chris Murphy
Image courtesy of Lawrence Lustig/PDC