Chris Rogers returned to haunt Gloucestershire as Middlesex stole a crucial march in the race for a Clydesdale Bank 40 semi-final place.
Needing victory to take charge of Group A, the Gladiators instead suffered a crushing 10-wicket defeat on the final day of the Cheltenham Festival, a result which casts doubt over their ability to qualify for the knockout stages.
So often a thorn in Gloucestershire's side during four seasons spent with Derbyshire, the 34-year-old Western Australian dominated proceedings at the College Ground.
Rogers smashed a century and sharing in a match-winning unbroken stand of 218 with Dawid Malan as Middlesex chased down a victory target of 215 with 9.3 overs to spare.
The result saw them move above Holland to assume leadership of the group.
None of Gloucestershire's bowlers was spared as Rogers made 122 runs from 102 balls to register his first one-day century for Middlesex, smashing 18 fours and a six in the process.
Malan proved equally uncompromising, cutting and pulling his way to a chanceless 89 from 81 deliveries with seven fours and four sixes to put the Panthers in control of the group.
Rogers and Malan's partnership was the highest for the first wicket in any one-day match for Middlesex, surpassing the 210 posted by Paul Weekes and Ed Smith against Northumberland at Jesmond in 2005.
Insufficient though it was, Gloucestershire's total of 214-8 was built around Dan Housego's enterprising innings of 68 from 67 balls.