Essex 149 for 3 (Cook 67*) beat Middlesex 148 (Porter 4-40, Walter 4-37) by seven wickets
Walter marked his List A debut on Wednesday with three wickets at the death against Sussex, and bettered that with four front-line Middlesex wickets for 37 from eight overs. At one stage he had taken 4 for 21 runs from 27 balls.
Porter weighed in, claiming his four wickets for 40 as Middlesex, put in, slumped from 54 for 1 to 117 for 9. Only a last-wicket stand of 31 between Steven Finn and Ravi Patel, the second best of the innings, took Middlesex to a seriously below-par 148. To compound their humiliation, they left nearly 10 of their 50 overs unused.
Alastair Cook saw Essex through to their fifth win in six as the day-night match ended with more than 20 overs remaining and still in bright sunlight. Cook finished unbeaten on 67.
The big news in Essex's selection was that James Foster came in for his first game of the season behind the stumps; he was on the scorecard as early as the seventh over. Nick Gubbins had hit five fours in 22 before he got a thick edge to Porter and a diving Foster took the catch in front of first slip.
After two brief breaks for rain, which enlivened the wicket no end, Middlesex lost two wickets in five balls. Nick Compton played on to Walter's second legitimate ball and then Dawid Malan wafted at Porter to give Foster a more straightforward catch.
Walter made deep inroads into the Middlesex middle-order in a spell of four wickets from 27 balls at a personal cost of 21 when he sent back Adam Voges, James Franklin and John Simpson in quick order.
Voges chased a wide one to give Foster a third catch, Franklin was trapped lbw on his crease next ball, and Simpson followed in his next over, also leg before. Middlesex had slumped from 54 for 1 to 90 for 6.
When the 22-year-old Walter came off after six overs, he had figures of 4 for 31. That brought Porter back into the attack and he claimed his third wicket, Ryan Higgins misjudging a slower ball and cross-batting to Tom Westley at short midwicket.
Tom Helm contributed just one before he sent back a tame caught-and-bowled to Ashar Zaidi and then Toby Roland-Jones fell lbw to Porter, stepping back and not playing a shot. Patel showed some spirit with a six off Zaidi over long leg as the tail wagged determinedly. , Patel finally departed for a pleasing 18 when he was bowled by Simon Harmer, leaving Finn 13 not out.
Varun Chopra and Cook moved comfortably to 49 for the first wicket. Cook stepped back to cut one from Helm and Chopra pulled Finn for two splendid fours before he was first to depart, caught behind on the drive against Patel.
Cook survived a dropped catch by Franklin in the slips off Finn when he was 35, and soon after Zaidi received a reprieve when Patel missed a simple caught-and-bowled on one. It only cost Middlesex five runs as Zaidi swept Patel low to Voges at square leg.
The England opener eased himself to fifty from 51 balls when he punched Patel through the covers for his eighth boundary. His ninth, though, was rather more fortunate as he edged Finn uppishly through a three-man slip cordon.
Tom Westley came in after successive first-ball ducks, but looked in better form as he thumped Finn through the covers for four and added two more with identical on-drives off Helm. However, in the same over, he chopped on and departed for 15.
Ravi Bopara looked in a hurry as he took three fours in an over off Patel, sweeping the first and lofting two straight drives to take Essex within 15 runs of victory in only the 26th over. The otherwise accurate Patel finished with a tidy two for 39 from his 10 overs.