Roberts scored the winner in Blackburn's previous two games but did not celebrate and his appearance in the second half against Tottenham spurred Rovers into a late rally.
"He is a player who wanted to make a statement and is doing very well at it," said Allardyce after Saturday's 4-2 Premier League defeat at White Hart Lane. "He has played his way back into the team.
"We said at the end of the transfer deadline: 'look you haven't got where you thought you were going to get.
'You thought you were going to get away and you haven't. So you are still a part of the team and if you prove you are the best player to play we will play you'.
"He is forcing his way in and is almost the number one selection for me."
Roberts certainly made a difference as Rovers scored two late goals but it was Blackburn's defensive woes that had Allardyce most annoyed.
"At 1-0 we had two of our best chances of the game and then going 2-0 down was the killer for us," he admitted. "We took control of the game in the first 20 minutes of the second half but failed to score.
"We then gifted Tottenham the third and it took the pressure off them. We created enough chances to have scored more. But unfortunately our defence failed to turn up."