KLM started flying to Mexico in 1952. Once weekly using a DC-6, a 32 hr flight [one-way]. I guess it made several stops en-route, but unfortunately I could not find those stops. It might very well be that New York was one of them.
I do know that in 1946 once weekly a New York flight would contiunue to Curaçao.
The first [trial] New York flight departed AMS
on 25 Feb 1946 by DC-4 Skymasyter NL
-305, with US captain McClure. Regular service [twice weekly] was started at 21 May 1946 by the DC-4-1009 "Rotterdam", captain was Evert van Dijk [who also flew the very same route 16 years before with Sir Charles Kingsford Smith in Fokker F.VIIB/3m "Southern Cross"]. The New York flights made en-route stops in Prestwick and Gander for a total travel time of 25 hrs 30 min [net flight time 21 hrs] one way.
[Idlewild] was not yet open to business at the time, and all KLM flights operating to New York were using North Beach Airport, which in 1947 off course became La Guardia Airport. I believe that KLM started using Idlewild [today JFK
] only in 1948, so KLM did operate transatlantic service into LGA
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"