Spurs were leading 3-0 and apparently coasting to their third win of the season after a dazzling opening 16 minutes, with Heung-min Son scoring after just 45 seconds and Harry Kane netting a fine double.
But it all went to pot in the closing stages in north London, as the battling Hammers scored three goals in the final EIGHT MINUTES to seal an unlikely point and 3-3 draw.
Manuel Lanzini's stunning stoppage-time strike completed a comeback started by Fabian Balbuena and a Davinson Sanchez own goal, with David Moyes leaping with joy on the touchline.
Bale made his long-awaited return to the Spurs side after seven years away as a second-half substitute when it was still 3-0.
But rival fans were heralding the return of 'the curse of Bale', as his introduction appeared to be the catalyst for Tottenham's capitulation.
The Welshman did go close to finishing off the game with what would have been a brilliant to make it 4-2, but after beating two defenders with quick feat he could only sidefoot the ball narrowly wide of the post.
And Mourinho insisted Bale's arrival didn't affected his team's performance negatively.
"Don't think so, honestly don't think so," said the boss.
"The decision not to start him was I think a good decision. A decision to show that he doesn't have a beautiful chair waiting for him in the team and he sits there the first time he can.
"It was a message to the team that in this team everybody has to fight for positions.
"He's very well accepted in the group. Everyone likes him, and I believe he also likes what he found here. So everything is positive and the focus was not on him.
"The focus was on the game and he was on the bench for 65 minutes or so and I don't think so, I don't think at all. It's a pity that he couldn't score that fourth goal which was a beauty and would have killed the game. But that's football."
Instead, not the first time, Mourinho admitted his players are not mentally strong enough after their late, late collapse against their London rivals.
"I think you can imagine how frustrated I am and how frustrated the players are, but that's football," added the Tottenham manager.
"It was exactly when we were in control that we conceded the first goal and their belief went up.
"My guys were not strong enough to cope with it psychologically and in the last few seconds we lost two points.
"I have to analyse the second half and I have to do it internally but for you I prefer to say that football happened and praise West Ham's belief.
"It is not easy to be losing 3-0 and be dominated, to keep the belief. I knew they are a different team to last season, but to lose an advantage of three goals is a big punishment and eventually [it was] deserved.
"We should be stronger. In the second half West Ham risked quite a lot, pressing up and they gave us more space. We should get an occasion to win the game.
"We were not then good enough or strong enough to cope with the last 10 minutes."
Jose Mourinho didn't blame Gareth Bale for his team's late collapse against West Ham, and instead said his players are 'not strong enough psychologically' after their stunning draw at White Hart Lane.