Harry Kane scored a hat-trick to help send England Under-21s second in their European Championship qualifying group.
Michael Keane scrambled the ball home for the Young Lions in the fifth minute before Tottenham striker Kane took over the scoring duties with a 45th-minute penalty and two close-range efforts in the second half to seal victory.
San Marino goalkeeper Andrea Manzaroli was sent off after conceding the penalty when he brought down Liverpool's Raheem Sterling – who had earlier been booked for diving – in the box, with the home side bringing on substitute stopper Massimo Francioni at the expense of midfielder Lorenzo Liverani as a result.
The win was England's second in three games in qualifying Group One and moved them up behind Finland with a game in hand.
England totally dominated the game and San Marino had no answer once they had been reduced to 10 men. Keane's opening goal proved to be the starter to Kane's main course, the 20-year-old Manchester United defender reacting quickly to re-direct Sterling's low drive. The opener set the tone and Sterling, Morrison and Tom Ince went close to doubling England's lead in the first half.
Francioni was kept busy after the break, denying Morrison, but Kane did find a way through in the 66th minute when he followed up his parried shot from close range, before grabbing his third off Tom Carroll's cross from the right.
England Butland; Stones, Jenkinson, Carroll, Dier; Keane, Ince (Redmond, 70 mins), Ward-Prowse, Kane; Morrison (Lingard, 55), Sterling (Ings, 65). Substitutes not used Chalobah, Long, Zaha, Berahino.
Referee Eiko Saar.