Since a 1-0 reverse at Heerenveen in late September, Phillip Cocu's men have won 14 and drawn one of their 15 league outings.
That sequence has seen them move 15 points clear at the summit, with second-placed Ajax - who have won the past four titles - visiting Go Ahead Eagles on Sunday.
Narsingh and Depay struck in a four-minute spell shortly after half-time at the Philips Stadion, before Yassin Ayoub pulled one back with 20 minutes remaining.
Depay then put the result beyond doubt in stoppage time with a low free-kick as PSV racked up a ninth straight league win.
Behind Ajax in third are PEC Zwolle, whose four-match unbeaten run came to a crashing halt with a 4-0 thumping at Heerenveen.
Luciano Slagveer, Sam Larsson and Mark Uth put Heerenveen in command at the interval, with Henk Veerman adding a fourth late on for the hosts, whose unbeaten streak stands at eight games.
Elsewhere, Excelsior prevailed 3-1 at Twente, while Bertrand Traore's goal handed Vitesse a 1-0 win at NAC Breda and the clash between bottom club Dordrecht and ADO Den Haag ended goalless.
