The win lifted United back above Liverpool in the race for Champions League qualification - five days before the fierce rivals meet at Old Trafford.
Chelsea lost in Manchester for the second straight weekend, defeated 1-0 at runaway leader Man City to drop five points adrift of the top four with nine games remaining.
It was Newcastle manager Rafael Benitez's first defeat in six games against Liverpool since he guided the Anfield team to Champions League glory in 2005.
Son made sure of victory in the 54th when he finished off a fine move by Tottenham, just moments after goalkeeper Hugo Lloris saved well from Tom Ince at the other end.
Arsenal squandered an early chance to get back into the match in the second half when Pierre-Emerick Aubameyang's penalty was easily saved.
Lukaku's 39th-minute equaliser, canceling out Willian's opener, was his first goal against any of the division's leading eight sides this season.
Tottenham were two points behind second-place Liverpool, with fellow top-four rivals Manchester United and Chelsea meeting later on Sunday.
Liverpool, the only member of the top six to play on Saturday, moved a point ahead of Manchester United, which hosts fourth-place Chelsea on Sunday.
Eden Hazard and Victor Moses' strike helped as Chelsea returned to fourth place and West Brom remained stranded at the bottom, seven points from safety.
The winger refused to sign a new deal with Arsenal and was highly speculated to reunite with his former boss Pep Guardiola in Manchester City.
The winger has made a bright start as he scored on his debut and Sanchez has set a new record on social media as the deal announcement post was 'the biggest United post on Instagram'.
Chelsea has lost three of its last four games in all competitions, and sits fourth in the league, a point above Tottenham.
Conte has been agitating and moaning for months about his failure to exert control, particularly over transfers.
Arsenal's Pierre Emerick Aubameyang scored on his debut where as Mkhitaryan assisted thrice as Arsenal demolished Everton 5-1.
After 18 months of speculations, Ozil finally pens down a new deal with Arsenal that will keep him with the club till 2021 as his existing contract with the Gunners had been due to expire by the end of the season.
The 2017-2018 winter transfer window has seen the top names being signed by the top dogs of the Premier League this season. Take a look.
United conceded inside 11 seconds to Christian Eriksen and was beaten 2-0 by Tottenham at Wembley Stadium in front of a record Premier League attendance of 81,978.
Aubameyang will compete with, or maybe complement, offseason signing Alexandre Lacazette up front as Arsenal look to make up an eight-point deficit to the Champions League qualification positions in the Premier League.
With players such as Paul Pogba, Nemanja Matic and Ander Hererra being the first names on the team sheet, Mata's starting days are mostly but over but Mourinho has always relied on the Spaniard to deliver.
City have spent about 120 million pounds (then $155 million) on three fullbacks Kyle Walker, Benjamin Mendy and Danilo in the last transfer window.
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