The former Republic of Ireland Under-21 midfielder had scored a late winner for the Terriers in their Yorkshire derby against Leeds at Elland Road last week.
Collins followed that up with his third goal in as many games to condemn Brighton to a hat-trick of defeats in all competitions.
Collins struck the decisive blow five minutes into the second half. Brighton defender Andrew Whing failed to deal with a cross from Keigan Parker and Gary Roberts knocked the ball back in for Collins to convert from close range.
Brighton, knocked out of the FA Cup in a replay at Hartlepool after defeat at Carlisle United, can count themselves unfortunate not to have picked up at least a point.
They had the better of the first half and went close to opening the scoring in the 24th minute.
Top-scorer Glenn Murray appeared to handle the ball just outside the box but, when Nicky Forster headed back to him, his volley with the outside of his right foot hit the top of the crossbar.
Micky Adams' struggling side endured similar frustration after the break. They had several half-hearted penalty appeals rejected by Steve Cook before the Surrey referee eventually pointed to the spot in the 74th minute.
Jonathan Worthington bundled over Forster as the Brighton skipper made progress into the area.
Forster took the penalty himself but Matt Glennon made a fine save, diving to his right, and Bradley Johnson could not force home the rebound.
Johnson, on loan from Leeds, went close to equalising in the closing stages with a well-struck free kick from 35 yards which also clipped the top of the bar.