On the day Andre Villas-Boas was sacked by Chelsea, Sir Alex Ferguson's second-placed side moved to within two points of table-topping City after a ruthless display of finishing at White Hart Lane.
United survived a strong showing from Spurs in the first half and took the lead through Wayne Rooney's header just before the break.
Young bagged the second with a powerful volley from a tight angle and then put the result beyond doubt with a stunning curling effort from outside the area.
Jermain Defoe reduced the deficit late on but third-placed Spurs have now lost their last two league games and are just four points ahead of resurgent Arsenal.
Ferguson felt United were fortunate to win and said: "I don't know how you explain it. We certainly carried a lot of luck.
"It was a great performance by Spurs in the first half. Maybe we got tactics wrong.
"We had a bit of luck scoring right beore half-time with our first effort on goal. That was a killer for Tottenham.
"We improved after half-time but it really needed the second goal to give us confidence.
"It was a massive result and a massive performance by our defenders. They have dug in and we showed the determination to get the result."
Spurs, without Gareth Bale through illness, injured Rafael van der Vaart and suspended Scott Parker, were denied a first-half opener when Emmanuel Adebayor's close-range effort was disallowed for a handball by the Togo striker.
United took full advantage of that let-off to take the lead themselves as Rooney got in front of Kyle Walker to head in Young's corner on the stroke of half-time.
Young got the second in the 60th minute as he lashed in a volley after Walker failed to clear Nani's cross and the England winger struck again nine minutes later, bending a fine finish past Brad Friedel as the Spurs defence backed off.
Defoe pounced on a wayward Ryan Giggs pass to lash home for the hosts in the 87th minute but it was no consolation for Harry Redknapp's side.
"I couldn't believe we were 1-0 down at half-time. I felt we were outstanding in the first half," Redknapp said.
"We've all had days when you walk off thinking, 'How did we win that?'. I'm sure Alex was thinking that today."
In the day's other games, Newcastle United drew 1-1 with local rivals Sunderland and Fulham routed struggling Wolverhampton Wanderers 5-0.
Shola Ameobi pounced from close range to deny 10-man Sunderland a first win at St James' Park for more than 11 years and extend his remarkable scoring record in the Tyne-Wear derby.
The 30-year-old forward's seventh career goal against the Black Cats earned a share of the spoils after Nicklas Bendtner's first-half penalty opened the scoring for Sunderland.
Martin O'Neill's side negotiated the last half-hour a man down after Stephane Sessegnon earned a straight red card for elbowing Cheick Tiote as the pair tussled for possession, though any contact looked light.
Simon Mignolet's stunning late penalty save had looked like putting a dent in Newcastle's European aspirations, the Belgium goalkeeper diving low to his left to keep out Demba Ba's 83rd-minute spot-kick, before Ameobi's late intervention.
At Craven Cottage, Russian striker Pavel Pogrebnyak hit a hat-trick as Fulham piled on the misery for struggling Wolves.
Cottagers boss Martin Jol signed Pogrebnyak on loan from Stuttgart on transfer deadline day to fill the void left by Bobby Zamora's move to QPR and it has proved an inspired piece of business.
After scoring in his previous two appearances, Pogrebnyak tore into the Wolves defence with two first-half goals and completed his treble after the break.
Clint Dempsey added a second-half double to ensure Wolves were sent home in utter despair after a run of just one win in 13 league games dropped them into the relegation zone, below Blackburn on goal difference.
Source: AFP
Source: AFP