The six times world champion took the chequered flag at Imola 5.783 seconds ahead of team mate Valtteri Bottas, who started on pole position.
Red Bull's double World champion Max Verstappen won the Mexico City Grand Prix on Sunday to set a Formula One record of 14 victories from a single season, as well as the most points scored.
Formula One world champion Lewis Hamilton took pole for Mercedes at the season-opening Australian Grand Prix.
Mick Schumacher made his first track appearance as a fully signed-up Formula One driver on Friday
Red Bull closed the gap to champions Mercedes in the constructors' standings to one point.
Hamilton decided to take matters into his own hands and pass several cars ahead of him, without gaining anything as Verstappen's time stood the test.
Red Bull's Max Verstappen went fastest in Styrian Grand Prix practice, on Friday, while Australian Daniel Ricciardo crashed his Renault
Monaco's Leclerc, who had started on pole position for the first time, lost power with 10 laps to go while leading and finished third with an extra point for the fastest lap.
Seven-time world champion Lewis Hamilton overtook main rival Max Verstappen and Mercedes team mate Valtteri Bottas to win the Portuguese Grand Prix on Sunday and go eight points clear in the Formula One standings.
Mercedes set for proper fight with Ferrari in Melbourne
Conor McGregor said on Tuesday he was retiring from the sport, five months after losing to Khabib Nurmagomedov in a controversial title fight
Verstappen took his 26th career win 0.9 of a second ahead of Spaniard Sainz,
Lewis Hamilton became the first Formula One driver to win 100 races with a victory in Russia that sent him back on top of the championship.
Lewis Hamilton won a crazy, twice-halted Saudi Arabian Grand Prix for Mercedes on Sunday to go level on points with Red Bull rival Max Verstappen and set up a winner-takes-all title showdown.
Hamilton said he only realised the significance of what he had done when he came into the pitlane after taking the chequered flag.
Ferrari's Charles Leclerc qualified third with team mate Sebastian Vettel a distant seventh on a distinctly off day for the German.
While 40-year-old racers were relatively common in the sport's early days, they are a rarity in modern Formula One with an increasing emphasis on youth.
Valtteri Bottas won the Azerbaijan Grand Prix on Sunday and retook the Formula One lead from team mate Lewis Hamilton after a fourth successive one-two finish for Mercedes.
The pole was the second of the Dutch 22-year-old's Formula One career and the first in Brazil for engine partners Honda since the late triple champion Ayrton Senna in 1991 with McLaren.
The front row lockout was a record-equalling 65th for champions Mercedes.
Formula One team bosses backed the decision of Japanese Grand Prix organisers to cancel all of Saturday's practice and qualifying sessions as the sport hunkered down to ride out Typhoon Hagibis.
The Dutchman won a maiden Formula One title after a last-lap overtake on Mercedes rival Lewis Hamilton in Abu Dhabi.
Lauda was so badly injured in that accident at the 1976 German Grand Prix that a priest gave him the last rites as he lay in a coma.