Collins struck ten minutes into the second half to scrub out Gary O'Neil's 16th minute opener and deny Portsmouth boss Harry Redknapp a crucial victory against his former club.
Redknapp's misery was compounded when Laurent Robert was sent off for his second booking six minutes from time.
Redknapp was facing the Hammers for the first time since he was sacked five years ago. He restored Uruguayan international Dario Silva to the starting line-up in place of the injured Vincent Pericard.
Silva almost marked his recall in the perfect fashion in only the second minute when his close-range shot was saved by West Ham goalkeeper Roy Carroll after turning centre-back James Collins on the edge of the penalty area.
Pompey had a strong claim for a penalty waved away in the 11th minute.
The tricky Lomana LuaLua looked to have been brought down by England left-back Paul Konchesky but referee Alan Wiley waved away the home side's appeals.
Hammers manager Alan Pardew made the first of three enforced substitutions in a fraught first half when Hayden Mullins was replaced by Carl Fletcher in the 12th minute.
The visitors barely had time to reshape before O'Neil opened the scoring with his second league goal of the season four minutes later.
LuaLua and Robert combined beautifully down the right before the Frenchman crossed for O'Neil to thump the ball past Carroll from 14 yards out.
Redknapp had an injury problem of his own in the 20th minute when Linvoy Primus limped off with a groin problem to be replaced by Danish international Brian Priske.
Pompey should have doubled their lead in the 22nd minute when captain Dejan Stefanovic somehow failed to connect to Robert's pinpoint free-kick.
The Hammers had another nervous moment in the 25th minute when Carroll came racing out of his goal and appeared to handle outside the area.
Television replays proved inconclusive but referee Wiley adjudged the ball to be just inside the penalty area.
Pardew was forced to shuffle his pack again 12 minutes before half-time when the injured Tomas Repka was replaced by Danny Gabbidon.
But Gabbidon's afternoon lasted only six minutes before the Welsh international was forced off with an occurrence of a knee injury and was replaced by Christian Dailly.
Robert ended the half by picking up his first booking for a late challenge on midfielder Matthew Etherington.
West Ham could have been level within two minutes of the re-start when substitute Dailly headed just wide after finding himself unmarked from Shaun Newton's corner.
Carroll gave the Hammers the jitters again two minutes later when he spilled Matthew Taylor's tame long-range shot but managed to redeem himself before LuaLua could reach the rebound.
LuaLua tested the Northern Ireland International once more in the 52nd minute when his 20-yard strike was gathered at the near post.
Marlon Harwood thought he had equalised for the Londoners soon after when his long-range effort came crashing back off Jamie Ashdown's right-hand post.
The Hammers did not have to wait long for their equaliser and it came courtesy of Collins' first goal for the club following a summer move from Cardiff.
Newton's right-wing corner was headed down by Anton Ferdinand for Collins to turn neatly and pick out Ashdown's bottom right-hand corner.
Newton should have made it 2-1 less than 120 seconds later when he seized on Andy Griffin's poor backward header.
But the former Charlton winger lost his footing at the vital moment and blazed harmlessly over.
Dailly came close again 15 minutes from the end when he again found himself unmarked inside the Pompey penalty area but headed over the bar from Etherington's centre.
Pompey's hopes of earning a much-needed victory disappeared when Robert received his marching orders for scything down Konchesky on the edge of the box.