Morgan swept his side past Surrey’s 50-over total of 286 for six with a breathtaking assault which saw Middlesex score the last 101 runs of their 292 for four from a mere 8.5 overs to win with 31 balls in hand.
In all, Morgan hit five sixes and 13 fours – reaching his 12th List A hundred with a six off Tillakaratne Dilshan and also finishing the match by swinging Zafar Ansari into the Warner Stand for a maximum.
His performance overshadowed the earlier batting of Dilshan, who made 115 from 128 balls to ensure Surrey posted a challenging total.
The 44th over of the innings, bowled by Dilshan, disappeared for 22 runs as Morgan clubbed the Sri Lankan for two more fours and two sixes.
Morgan was joined in an unbroken partnership of 166 in 20.3 overs for the fifth wicket by Neil Dexter, who also batted well to finish on 47 not out from 58 balls with a six and three fours.
But Dexter’s own effort was nothing compared to Morgan’s fireworks, which meant Middlesex could at last celebrate some limited-overs joy.
They began their Royal London Cup Group B campaign with two defeats, against Glamorgan and Warwickshire, after losing 11 of their 14 NatWest T20 Blast group games earlier this summer.
Yet when Middlesex slid to 126 for four in the 25th over, despite Chris Rogers’s 44-ball 42 at the top of the order, it seemed as if they would be hard-pressed to win the game.
Rogers top-edged a sweep at Dilshan’s off-spin, stalling Middlesex’s reply after he and Dawid Malan provided a sound start with a 56-run stand in nine overs.
Nick Gubbins was then run out for 20 and Ryan Higgins gave left-arm spinner Ansari a return catch on 16. Morgan and Dexter, however, made the remaining chase look ridiculously easy.
Earlier Dilshan’s hundred, his first for Surrey, anchored the innings and was a skilful effort featuring 11 fours. He was joined in stands of 119 for the second wicket and 81 in eight overs for the fifth by Vikram Solanki and Azhar Mahmood respectively.
Solanki launched Dexter’s medium pace over long-on for six and there were also seven fours in his 80-ball 59, while Mahmood provided late impetus with 52 from just 34 balls.
The former Pakistan all-rounder drove left-arm spinner Ravi Patel straight for six besides thumping seven meaty fours before he skied an attempted big hit off Steven Finn to wide long-on.
Steven Davies went early for Surrey, edging Tim Murtagh to slip on 13 as he tried to force the ball away on the back foot, and, after the Dilshan-Solanki partnership was ended when the latter missed a sweep at Malan’s leg-spin, the innings wobbled a little as Rory Burns was run out for nine and Gary Wilson caught behind for 10.
Burns slipped in mid-pitch after being sent back by Dilshan and Morgan’s flipped throw from midwicket, as he lay on the turf following a smart stop, hit the stumps before the batsman could regain his feet.
Mahmood’s arrival pushed Surrey on and, by the time Dilshan was out in the 47th over, edging a slash at the impressive Finn to the wicketkeeper, Surrey knew they would be defending a decent total. They had no answer at all to Morgan’s brilliance, though.
Middlesex captain Morgan was delighted with the result, and said: "Games against Surrey are always competitive, so it's great to be able to produce it against them. That's one of the highlights of my Middlesex career.
"This last month has really tested us with the schedule we've had and being on the wrong end of so many results in one-day cricket. But to stick at it and win today is testimony to the character of the players we have in our squad."