United - trailing 2-0 to Spurs at half-time - were handed a lifeline early in the second period after Webb adjudged goalkeeper Heurelho Gomes to have fouled Michael Carrick inside the danger-zone, with replays showing the glove-man clearly won the ball.
Cristiano Ronaldo despatched the spot-kick, with the Premier League holders going on to run riot against their flabbergasted opponents, scoring another four to complete the unlikeliest of 5-2 victories.
And Jenas believes the match official's dubious decision was a result of him buckling under the weight of a vociferous crowd at the Theatre of Dreams.
"That was a prime example of a referee crumbling over the pressure at Old Trafford," he said in the Mirror.
"I don't want to make excuses and we went on to concede another four after that, which were sloppy goals, but it would have been a completely different game had they not got that first goal.
"It's just the way football is sometimes and pressure gets to people. The atmosphere, the occasion, the importance of the match, a lot of factors take their toll when making decisions.
"One thing that struck me about it was that he didn't even think.
"It was like he'd already made his mind up when he came out for the second-half that he was going to give something."
NEWS: Webb admits to penalty gaffe
NEWS: Redknapp rages at Webb spot-kick shambles
UNITED FANS! Check FourFourTwo.com’s ever-expandinginterviewsarchive for more stuff to read:
Web Exclusives Wayne Rooney, Peter Schmeichel, Carlos Tevez
Q&A Wayne Rooney, Cristiano Ronaldo, Ruud Van Nistlerooy
One on One David Beckham, George Best
Ask A Silly Question Bryan Robson
Boy's A Bit Special Danny Simpson
Perfect XI Garth Crooks, Bryan Robson, Sir Bobby Charlton, Eric Cantona
What Happened Next? David May, Norman Whiteside
Sing When You’re Winning Dominic Monaghan, Ian Brown
And Another Thing Being a Big Four fan
Plus! Rate United players (and others) onTalentspotter
SPURS FANS! Check FourFourTwo.com’s ever-expandinginterviews archivefor more stuff to read:
Web Exclusives Les Ferdinand, Paul Gascoigne, Gary Lineker, Glenn Hoddle, Frederic Kanoute
‘He instantly popped into our ratings as one of the best U21 midfielders in Europe. The impressive thing is Slot has made him into more of a no.6' Inside Ryan Gravenberch's transformation at Liverpool
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
