The win leaves United in 15th place in the Europa League standings on six points from four games.
Napoli broke a three-decade long drought, to lift the Seria A title on Thursday. The last time Diego Maradona led them to the title in 1990.
But after an exceptional transfer window and with Luciano Spalletti at the helm, Napoli dominated the title race while their main rivals all suffered slumps during the season.
Images from the FIFA World Cup Group F match between Belgium and Morocco on Sunday.
Belgium's creativity and power proved too much for World Cup debutants Panama as the Group G favourites overcame the heroics of goalkeeper Jaime Penedo and a massed defence to run out 3-0 winners on Monday.
A round-up of matches played in the Serie A and French Ligue 1 on Sunday
Images from the World cup match between Belgium and Algeria.
Eriksen is recovering at a nearby hospital and will have an implantable cardioverter defibrillator
Belgium go into Monday's World Cup last 16 match against Japan full of confidence but wary that relying on individual talent against similarly well-organised but less fancied teams has cost them dear in the past.
Belgium begin their campaign in St Petersburg against Russia on June 12
Much-fancied Belgium fought back from a goal down to score twice in the final 20 minutes and earn a hard-fought 2-1 victory over gutsy Algeria in their World Cup Group H opener on Tuesday.
Napoli could become the first team in Champions League history to qualify from their group after only three games on Wednesday, providing welcome relief from their recent troubles.
AC midfielder Franck Kessie scored from a penalty to give AC Milan a 2-2 draw away to Napoli in Serie A on Sunday, sparing the blushes of his goalkeeper Gianluigi Donnarumma whose mistakes provided the hosts with both their goals. Sevilla closed in on Champions League qualification by beating struggling Real Mallorca 2-0 at home to open up a nine-point gap in the race for fourth spot in La Liga.
The youngest at Euro 2020 will be Poland's Kacper Kozowski - one of two 17-year-olds in the tournament, which has never happened before.
"I didn't do it before because I was young and I didn't have the profile I have now," De Bruyne, who turns 28 next Thursday on the same day Belgium play England in their final Group G fixture, told RTBF television.
News of all that's transpired on and off the football field
Serge Gnabry scored twice as Bayern Munich beat Chelsea 3-0, while Antoine Griezmann's second-half equaliser handed Barcelona a vital away goal and earned them a 1-1 draw at Napoli in their Champions League last 16, first leg on Tuesday.
Images from soccer matches played across different leagues in Europe on Sunday
Football action from across Europe in matches played on Saturday
Belgium strolled into the World Cup last 16 on Thursday after Jan Vertonghen's late goal gave them a 1-0 win over a South Korean side unable to take advantage of a 45-minute numerical advantage and who exit the tournament.
Carlo Ancelotti's side held a two-goal lead at halftime thanks to strikes from Dries Mertens and Kostas Manolas, but Balotelli pulled one back as Brescia rallied after the break.
The tournament debutants held their own against a highly rated Belgian side in the first half in Sochi before a stunning volley from Dries Mertens and a Romelu Lukaku brace after the break helped the Europeans climb to the top of Group G.
Coach Maurizio Sarri was sent off as Napoli wasted a chance to return to the top of Serie A when they were held 1-1 at home by AC Milan in a tense encounter.
Napoli squandered a two-goal halftime lead, then scored two late goals to beat nine-man AC Milan 4-2 in a stormy Serie A match which saw eight other players booked on Saturday.
A dipping long-range strike from Kevin de Bruyne gave Belgium a late 2-1 win away at 10-man Switzerland in a friendly between the two Euro 2016 finalists on Saturday.
Dries Mertens and Michy Batshuayi were also on target for Belgium while Eden Hazard impressed with creativity and speed for the hosts, who start their World Cup campaign on Monday against Panama in Sochi.
The FIFA 2022 World Cup will kick-off in Qatar on Sunday, November 20. Here is a list of the 26-man squads playing in the quadrennial global football extravaganza.
Galatasaray win 22nd Turkish title after beating closest rival
Champions Juventus lost for the third time in six Serie A matches this season after goals from Lorenzo Insigne and Gonzalo Higuain secured a 2-1 home win for Napoli on Saturday.
Belgium could make wholesale changes for Saturday's European Championship clash with Ireland as they seek to keep their tournament hopes alive, coach Marc Wilmots said. "Tomorrow there will be between two and 10 changes. Only the goalkeeper is certain," he told reporters, refusing to confirm a starting place for playmaker Kevin de Bruyne, who suffered a light injury in training on Thursday.
Christian Eriksen kept Tottenham Hotspur's hopes of completing a remarkable salvage job and reaching the last 16 of the Champions League alive with a late winner in his side's 1-0 victory over Inter Milan at Wembley on Wednesday.
Belgium coach Roberto Martinez declared himself delighted with a 3-0 win over World Cup debutants Panama but there were plenty of issues that will encourage England after their own winning start in Group G.
Defensive injury concerns for veteran squad leader Vincent Kompany and Barcelona's Thomas Vermaelen have eased and coach Roberto Martinez has sent standby defender Laurent Ciman home.
Veterans Arjen Robben (21) and Wesley Sneijder (34) laid the groundwork for a Dutch victory in coach Dick Advocaat's first game in charge.
Belgium and England have already met during the World Cup in a match both teams seemed reluctant to win and on Saturday they will face each other again in a game they both seem reluctant to play. The two sides must pick themselves up and dust themselves down after suffering the crushing disappointment of semi-final defeats to play for the modest prize of third place in a fixture often criticised as pointless.
A restaurant in St Petersburg has struck a chord with the hordes of soccer fans in town for the World Cup by serving up pizzas featuring the faces of some of the tournament's biggest stars.
Two goals each for Romelu Lukaku and Eden Hazard and one for Michy Batshuayi swept Belgium to a 5-2 victory over Tunisia on Saturday that put them in command of World Cup Group G.
The Chelsea playmaker gave Lukaku a piece of his mind in Sochi on Monday after Belgium had huffed and puffed but failed to blow Panama's modest defensive fortress down before the interval.
Manchester City swept aside second-tier Cardiff City 2-0 with first-half goals from Kevin De Bruyne and Raheem Sterling on Sunday to reach the FA Cup fifth round in their quest to win an unprecedented four trophies this season.
Marouane Fellaini played chief tormentor as France suffered a 4-3 home defeat in a home friendly against Belgium on Sunday.