Kane could not have asked for a more ideal start on an individual level, although England got lucky.
England controlled all the possession at the start of the second half, but for all their dominance they couldn't break down a resilient Tunisia defence.
Starting line-ups Tunisia: Mouez Hassen, Syam Ben Youssef, Yassine Meriah, Fakhreddine Ben Youssef, Ali Maaloul, Dylan Bronn, Ellyes Skhiri, Ferjani Sassi, Naim Sliti, Wahbi Khazri (capt), Anice Badri.
But Tunisia were gifted a way back into the game on 35 minutes, as Kyle Walker caught Ben Youssef with an arm in the England box and gave away a penalty.
Maguire nodded on a corner to the far post and Kane was there to glance home, to the delight of all connected to England. Though it was a narrow result, the team looked good in the final third when it came to passing and creating chances.
In four previous World Cup appearances, Tunisia have won only one game - against Mexico in 1978.
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Kieran Trippier and Young failed with free-kicks as England displayed a worrying lack of creativity, but they made up for it with their never-say-die attitude at the death.
Kane came to the rescue in the end, but England need to be better than this if they have to have a chance of reaching the latter stages.
England's players later thought they deserved a similar call when Kane was brought down in the opposite penalty area, but the referee disagreed. In the first half, a John Stones shove on a Tunisia defender at a corner probably negated the rugby tackle on Kane seconds later.
Holding, shirt-tugging and grappling at set-pieces has become an increasing problem in the game in recent years, and one that Federation Internationale de Football Association has attempted to eradicate.
That moment looked like it would prove pivotal in this Group G opener, yet, in the first of four additional minutes, Kane popped up again and netted a crucial victor for Southgate's men, heading in from five yards to secure a late 2-1 victory.