Welker botched a catch while unguarded that would have given the Patriots a first down with 4:00 to play. Instead, New England punted away the ball and the New York Giants marched 88 yards for the deciding touchdown in a 21-17 triumph.
"It hit me right in the hands. It's a play I never drop. I always make," Welker said. "Most critical situation and I let the team down."
Had Welker grabbed Tom Brady's pass with the Patriots clinging to a 17-15 lead, New England would have had a first down deep in Giants territory and could have run time off the clock, possibly scored, and ended the threat of a comeback by New York.
Instead, Eli Manning guided the Giants downfield and Ahmad Bradshaw scored on a six-yard touchdown run with 57 seconds remaining, leaving the Patriots enough time only for a desperate pass from midfield into the end zone on the last play.
Asked if the Patriots were guilty of squandering numerous chances to win the game, Welker said, "I'm right there at the top of the list."
"It's one of those plays I have made 1,000 times, just didn't make it. The ball was right there. I have got to make the play.
"It comes to the biggest moment in my life and I don't come up with it. It's discouraging."
Quarterback Brady backed Welker to get over the disappointment, saying he still has plenty of confidence in his favorite target.
"It looked like they messed up the coverage a little bit and I threw it to him," Brady said. "He went up to try to make it and we just couldn't connect.
"He is a hell of a player. I will keep throwing the ball to him for as long as I possibly can."
The Giants' late drive also put the Patriots in the unusual position of having to let Bradshaw score so they could get the ball back in time to have a chance at a game-winning drive.
New York moved near the goal line as the final seconds ticked away and could have taken the clock to near zero and then given kicker Lawrence Tynes a field goal try to win the game from point-blank range.
The Patriots preferred their chances of chasing a touchdown in the final seconds over Tynes missing the easy kick.
"We were trying to let them score," Patriots linebacker Jerod Mayo said. "That was the smart play to make. Situational football—let them score and get our offense back on the field.
"He was about to take a knee (short of a touchdown) but then he ended up going into the end zone, which worked in our favor, but we just didn't come up with it.