Or to put it another way:
11 Jan 1964: first win by own team in Tasman Cooper (NZ GP)
11 Oct 1964: first win by a McLaren (Riverside GP)
11 Oct 1964: first win by Bruce McLaren in his own team with his own car (Riverside GP)
I am intrigued by the discussion of the 1st McLaren sportscar win and would like to add my thoughts.
Bruce was one of the early aces at Mosport, and always ran near the front there. In June 1964 I saw him win with the much modified Xerox Special, diplomatically named a Cooper-Oldsmobile. In Sept of the same year he debuted the McLaren M1 at the Canadian Grand Prix. He dominated much of the race, but pitted for throttle linkage problems, handing the win to Pedro Rodriguez's Ferrari. This same car appeared a few weeks later at Riverside Oct 11, but did not win. Parnelli Jones won in the Cooper-Ford (King Cobra) while Bruce dnf with a burst hose. The Shelby Coopers also won at Laguna Seca the following week.
This puts the 1st win for the M1 into spring 1965. Looking at results lists and referencing Eoin Young's McLaren Memories, I conclude that the 1st win was by Charles Vogele in a customer McLaren-Elva as stated by Duc-Man The first of many McLaren team victories would be at Silverstone 15 May 1965, where Bruce won over Surtees's Lola-Chevrolet. This victory is rather downplayed by Young, considering it was the first team win in a car with McLaren on the nose, perhaps this is because of the earlier Vogele victory, or because a win was inevitable once teething problems were dealt with.