Middlesex 294 for 7 (McCullum 110, Malan 70, Ingram 3-38) beat Glamorgan 266 (Ingram 85, Rudolph 45, Fuller 3-53) by 28 runs
Brendon McCullum hit 110 off 85 balls and Dawid Malan produced a telling all-round display, scoring 70 and taking two wickets, the day after his England call-up as Middlesex secured a 28-run victory against Glamorgan in Cardiff.
Despite another masterful innings from Colin Ingram, who scored 85 from 73 balls, Glamorgan were beaten for the first time although they remain top of the table ahead of their break from this competition before resuming in the first week of August.
Middlesex, who were put in to bat on a good pitch, made a respectable 294 for 7, but after an opening partnership of 176 in 27 overs between McCullum and Malan, they would have expected to have reached a total in excess of 350.
On the ground where he scored 160 on his Championship debut for Glamorgan against Leicestershire 10 years ago, McCullum was soon into his stride, striking boundaries on both sides of the wicket, but he was reprieved on 49, when a leading edge was dropped off Craig Meschede at mid-off.
He then raced to his first century for Middlesex, but after scoring 110 from only 85 balls with 11 fours and five sixes he struck a full toss to long-off.
Earlier, Malan, who was named in England's T20 squad on Monday for the forthcoming game against Sri Lanka, played a composed innings of 70 before touching one to the wicketkeeper.
From a strong position, Middlesex then suffered a mid-innings collapse, as Ingram settled into an accurate 10-over spell with impressive figures of 3 for 38. Eoin Morgan played a laboured innings of 10 from 16 balls, which included eight singles, until he swept Ingram to deep square leg.
Glamorgan's bowlers were so effective that no boundaries were struck between the 30th and 46th overs, and it needed a partnership of 46 in 26 balls between Toby Roland-Jones and Ollie Rayner to boost Middlesex's total.
Needing to score at six runs an over, Glamorgan's openers Jacques Rudolph and David Lloyd made a rapid start, reaching 50 from the first ball of the eighth over with Lloyd striking Roland-Jones for three fours in his third over. He scored 41 from 29 balls, before pulling a short ball from James Fuller to Paul Stirling on the long leg boundary.
Rudolph and Will Bragg then added a useful 49 before Rudolph was caught behind from James Franklin's fifth ball of his opening over. Bragg soon followed and at the half-way stage Glamorgan required a further 174 with seven wickets in hand.
Franklin, obtaining movement from the River End, halted Glamorgan's progress and took his third wicket when Aneurin Donald wafted at one outside the off stump.
Ingram and Chris Cooke then settled in to their stand, playing every ball on merit, with Ingram reaching his third consecutive one-day fifty from 47 balls. With ten overs remaining, Glamorgan needed a further 87, but Franklin's gamble paid off when he brought Malan on to bowl his occasional legspin with Cooke holing out at long-on, and Meschede falling in similar fashion.
Ingram, however kept going until the 47th over when he drove Fuller to long-on and with him went his team's hopes of maintaining a 100% record.