The New York Mets have had seven walk-off grand slams in franchise history, one was by Tim Harkness (Montreal, Que.) who later managed the Toronto Maple Leafs in the Intercounty League.

From centrefieldmaz
A Historical Mets Blog site
Rmembering 50 + Years of Mets Baseball
1963: On Wednesday June 26th 1963, Tim Harkness hit the first walk off grand slam HR in Mets history. The game was in the 14th inning at the old Polo Grounds in New York. Galen Cisco had just gave up a two run inside the Park HR to the Chicago Cubs future Hall of Famer; Billy Williams. With the Mets now down 6-4 in the home 14th, Jim Hickman & Ron Hunt both singled, but Hickman was thrown out trying to go to third base. 

Next the wacky Jimmy Piersall drew a walk but slugger Frank Thomas flew out for the second out. Pitcher Jim Brewer was brought in & gave up a walk to Sammy Taylor to load them up. Harkness stepped in & hit a HR down the right field line, to win the game. 

It was Harkness’ 7th HR of the year & thrilled who ever was left of the 8,183 fans in attendance. Tim Harkness would only play two seasons with the Mets (four in the majors). In 1963 he saw the most playing time (123 games) batting just .211 with 10 HRs & 41 RBIs.

1963: Six weeks later, on Friday night Aug. 9th 1963, Jim Hickman hit the second walk off Mets grand slam. The game was in the Polo Grounds against the Chicago Cubs & tied 3-3 in the bottom of the 9th. The Cubs’; Paul Toth was still on the mound after making the start, nine innings earlier. With one out Jim Hicks singled, Cho Cho Coleman struckout & the Mets were down to the last out. But Al Moran doubled, putting two men on. Cubs manager Bob Kennedy brought in Lindy McDaniel to close it out. 

The Cubs remembered what Tim Harkness had done to them a little over six weeks ago & weren’t going to let it happen again. They gave him a free pass to first, bringing up Hickman with the bases loaded. Hickman blasted the grand slam & the Mets had a 7-3 win for the 11,566 fans in attendance. Jim Hickman led the Mets in HRs in 1963 with 17 & was second in RBIs with 51 batting just .229.