Smalling: Looks to have a promising future at Old Trafford
The 21-year-old centre-back has been rewarded for an impressive debut season at United, during which he made 33 appearances as they regained the Premier League title.
The England Under-21 international established himself as a reliable understudy to first-choice pairing Rio Ferdinand and Nemanja Vidic following his summer switch from Fulham.
And Smalling is set to enjoy more opportunities next term with John O'Shea and Wes Brown having moved to Sunderland.
"I am delighted Chris has signed a new contract," United boss Sir Alex Ferguson told the club's official website.
"Chris has been outstanding since joining us from Fulham last year.
"He is an extremely talented young defender, he's quick, strong and reads the game well. He is a great asset to the team."
Smalling arrived at Old Trafford on a four-year deal and had no hesitation in extending his contract to 2016.
"This is a great club and, in the short time I have been here, I have already achieved more than I could have ever expected to," he added.
"I am looking forward to a long and successful career at Manchester United."
Old Trafford bosses were already preparing contract reviews, which would see their pay shoot to £40,000 a week, before Monday's heroics in the home win against Spurs.
Striker Welbeck, who scored one and crafted another in the 3-0 win, has little under two years remaining on his existing terms.
Both he and midfield ace Cleverley, who only signed a three-year extension last summer, are currently two of the lowest-paid in United's first-team squad.
But SunSport understands that the Red Devils plan to sit down with the players' respective camps over the next few weeks to sanction the improved terms. It will go a long way to protecting their investments and give further proof they have long-term futures at the Old Trafford club.
Welbeck, 20, and 22-year-old Cleverley's pay hikes will bring them in line with fellow rookie Chris Smalling, 21, who recently agreed terms until 2016.