Mets closer Frank Francisco began his rehab assignment with Double-A Binghamton today, starting his rehab one day later than initially planned.

Francisco was very rusty, allowing one run on three hits, a walk and a strikeout in 2/3 of an inning.

Francisco threw 24 pitches, 14 of which were strikes.

Francisco, who has been on the disabled list since June 23 with a strained left oblique, was slated to begin his rehab on Tuesday with Class A Brooklyn, but discomfort in his right knee — that ultimately required a shot — pushed his schedule back a day.

Francisco says he felt no pain in his knee or any soreness in his oblique.

“We need him back very badly. Our bullpen has had a tough time,” manager Terry Collins said. “He’s the one addition. You’re trying to find bullpen help, we’ve got bullpen help. It’s in-house. We just got to get him back out there.”

Francisco could be back during the west coast swing. He has a 4.97 ERA and a 1.59 WHIP in 31 appearances with 18 saves for the Mets this season.