On a night when Gareth Southgate could have dispensed with defenders altogether, England toyed with FIFA's lowest-ranked nation who rarely got past the halfway line in the Group I game.
They might be disappointed, however, that San Marino goalkeeper Elia Benedettini only had to pick the ball out of his net five times despite England's 32 attempts at goal.
San Marino held out for 14 minutes before James Ward Prowse opened his England account and Calvert-Lewin made it 2-0 seven minutes later. Raheem Sterling, who missed a succession of early chances, got the third goal just after the half-hour at which point it seemed England might be heading for double figures.
To their credit San Marino's part-timers dug deep in the face of a siege at Wembley with Calvert-Lewin's second goal after the break, a tap-in, the only addition to the score until substitute Watkins slotted in late on.
"I think we did as well as we could, really," Southgate, who fielded a largely second-string side, said. "Of course it's an opponent we should beat, but I thought we played really well.
"The midfield moved the ball really well. It was good to see (the recalled) Jesse (Lingard) enjoying his football again. It was nice to give Watkins half an hour and for him to get a goal is a fairytale."
In the 31 years since San Marino, the world's smallest republic, have played in FIFA and UEFA competitions they have never won a game, while in their previous six meetings with England they had conceded 37 goals.
They had kept clean sheets in two of their last three games, against Gibraltar and Liechtenstein, and set out with only one aim which was to try and keep the score respectable.
That they did so against a largely second-string England team was mainly down to Benedettini, who plays in Italy's third tier, for making numerous outstanding saves.
Lingard, restored to the England team after an impressive loan spell at West Ham United, would have been sick of the sight of him by the end of the night as he was denied on several occasions, including one flying save early on.
Ward-Prowse had got the scoreboard ticking with a clinical left-foot finish from Ben Chilwell's cut back and it was Chilwell's Chelsea team mate Reece James whose inviting cross allowed an unmarked Calvert-Lewin to head his first goal.
England's third was a gift for Sterling after San Marino gave the ball away. Eight minutes into the second half Chilwell played in Lingard down the left and his pass was gift-wrapped for Calvert-Lewin to make it 4-0.
After that it was a training ground routine for England as Ward-Prowse pinged a free kick against the woodwork.
Watkins made sure it was a memorable night for him though as he drilled in a clinical low shot in the 83rd minute.