Khazri and Dylan Broon scored for Tunisia but it was not enough as they were eliminated from the tournament.
Roberto Martinez's side stormed their way to a 5-2 victory and are now on the verge of reaching the last-16 stage.
Belgium keeping the ball well now but Tunisia challenging on the counter. Ronaldo has scored four goals in Portugal's first two games.
In addition, Eden Hazard's converted spot kick is the 13th penalty awarded at this World Cup.
Reports of attempt on Zimbabwean President Emmerson Mnangagwa’s life
An explosion has rocked a stadium in Zimbabwe where the nation's President Emmerson Mnangagwa was addressing a rally on Saturday. Bulawayo has always been a bastion of opposition to the ZANU-PF and it was Mnangagwa's first rally in the city.
Lukaku doubled the lead for the Red Devils in the 16th minute with a low strike after going through on the left side of the box, 2-0.
Earlier, Eden Hazard opened the scoring from the penalty spot before Lukaku made it 2-0 for Belgium.
That would leave their meeting in Kaliningrad on Thursday to decide who tops the group and it is Belgium who hold the upper hand there, with their sparkling finishing in the sunshine at the Spartak Stadium leaving their goal difference significantly better off.
Tunisia are effectively out of the competition after two defeats.
Optus Handing World Cup Group Matches To SBS After Total Failure
Optus chief executive Allen Lew apologised "unreservedly to all Australians" on Sunday, but there were further issues later that night.
Numerous favorites in the 2018 World Cup have disappointed, but until Argentina fell 3-0 to Croatia on Thursday, Germany was the only one to suffer a defeat.
Substitute Batshuayi missed a hat-trick of fantastic chances within five minutes before finally finding the target in the 90th with a good finish.
Belgium has all but qualified from Group G with two wins.
Dries Mertens won possession just inside the Tunisia half before driving forward and feeding Lukaku.
'He was hiding away on his own up front in the first half.
Beyoncé And Jay-Z Take Over The Louvre In 'APES**T' Video
In the album's track Nice, Beyonce raps: "If I gave two fucks about streaming numbers / would have put Lemonade up on Spotify ". Everything Is Love dropped without warning yesterday, though Jay-Z had previously alluded to the existence of a joint album.