Mateo Joseph's close-range tap-in sent the hosts behind but Ben Parkinson's impressive finish - the 17-year-old's first goal at under-21 level - drew Newcastle level before Leeds restored their one-goal cushion a minute later through Charlie Allen's bundled effort.
A frantic finale saw Connor Ferguson's own goal level the Division Two clash before Newcastle held firm in the final minutes after Remi Savage was shown a controversial red card for a last man challenge on Luca Thomas.
Diallo, who signed his first professional contract with the Magpies in October, following a successful trial, said: "I thought the boys showed good spirit to come back in the second-half. I think we should have played like that for the full game as the first-half was a bit slow.
"We got going in the second half and I thought we could have won the game. We need to build on this now and try to win our next game. I see it everyday in training that the lads don't give up so I expected us to try and come from behind and everyone played their part in the game to do that.
"I thought we deserved the win even when we went down to ten men. The red card was a bit harsh as it looked like the (Leeds) player tripped himself up and went down.
"It was a great save from Thommo (Max Thompson) from the free-kick which helped us. We still stuck together as a team, defending well, to see the game out. It gives us a lot of confidence going forward because Leeds are second in the table."
After spending a decade at West Ham United's youth set-up, Diallo revealed he has been relishing his time at Newcastle's Academy since arriving earlier this term.
The former England under-17 international, who celebrates his 20th birthday on Wednesday, has started the young Magpies' last five competitive fixtures and believes he is continuing his development both as a player and person since moving from East London to Tyneside.
The teenage winger, who primarily plays on the left flank, added: "I'm enjoying my football. I'm getting my confidence back and just working hard to try and help the team.
"That's all I can do and I thank the coaches for giving me the opportunity. I feel I am getting better defensively and being more tactically aware in the games because of them.
"As a person, I've changed a lot because I live alone, away from my family, so I've been more independent which has been a big positive in growing up.
"I've enjoyed living in Newcastle. Everyone is very friendly around here and I like going to watch the first-team play at St. James' Park. The atmosphere is lively!"
