Train service to Montauk and the Hamptons will be restored just in time for Memorial Day, MTA officials promised on Sunday.

The Long Island Rail Road announced full service to the Montauk Branch for Monday following a train derailment that halted operations to the popular East End destinations early Saturday.

LIRR service on the Montauk line had been suspended east of Patchouge since a Montauk-bound train sideswiped an empty locomotive near Speonk about 1 a.m., according to the MTA.

Three trains in total — a passenger train and two locomotives — derailed during the crash that heavily damaged the track and destroyed key operating equipment.

Nobody was injured.

The LIRR had provided passengers traveling to the South Fork on Saturday and Sunday with bus service from Patchouge to Hampton Bays, and then a shuttle train back and forth to Montauk.

Crews over the weekend worked round the clock to re-rail the trains, repair destroyed switches and signals and rebuild hundreds of feet of track, the MTA said.

Monday’s restored service will operate on a Holiday schedule.