McTominay strike earns Napoli victory at Torino
The result left Antonio Conte's side four points clear at the top of the table, while Torino is 12th and now just four points above the relegation zone.
McTominay broke the stalemate with a moment of quality in the 31st minute, having received a wonderful pass from Khvicha Kvaratskhelia.
The second half was comfortable for the league leader, which could have extended the lead after chances fell to Romelu Lukaku and Mathias Olivera.
Torino's defeat, its seventh in nine matches, saw it drop further towards the relegation picture in Serie A.
It is now just four points ahead of third-bottom Como ahead of a trip to midtable Genoa next weekend.
Napoli, meanwhile, opened a four-point gap between itself and second-placed Atalanta, which plays on Tuesday (AEDT) against Roma.
Conte was pleased Napoli responded to his plea for improvement by claiming the win.
"I have a group of guys who really understand when I ask them to improve. This is the aspect I like the most, beyond the result and the standings," Conte said.
"We are growing as individuals and as a team... Torino are a great team. I was really afraid of this game. I lived in Turin for more than thirty years. I warned the guys, [and got] a mature response.
"Sometimes you take refuge in the result. Today we created, but there was a great goalkeeper who prevented us from being more relaxed at the end," Conte added.
Conte had praise for McTominay, too, after the former Manchester United man's match-winning effort.
"He is a boy who was not a protagonist at [Manchester] United. I knew him well because I frequented the Premier League, he has quality," Conte said.
"We were lucky because he agreed to come in a situation in which we were not playing in Europe, having finished in 10th place. He could have seen Napoli as a demotion, instead, he came to be a protagonist."
Despite his satisfaction with the result and his side's growing form, the Italian coach pointed out that Napoli will need reinforcements if it keeps up its good form and return to Europe next season.
"Looking at the other teams, how they've equipped themselves also in view of the commitments in Europe, and if we were to be good at getting into Europe, you will have to strengthen this squad... The president must know that," he said.
"Today we have 21 outfield players, and we have done what a team that only plays in the league and the Italian Cup does."
Scott Francis McTominay
SSC Napoli