Lehane came on for the injured Anthony Elding in the 20th minute but linked up superbly with fellow striker Mark O’Sullivan throughout to give the Limerick defence all kinds of problems.
City boss John Caulfield made three changes from the side that drew 1-1 with St Pats’s on Friday night, with Darren Murphy, O’Sullivan and former Limerick player Dave O’Leary coming in for Gearoid Morrissey, Garry Buckley and Colin Healy.
Limerick boss Stuart Taylor started with the 11 that drew 0-0 with Bray Wanderers at Thomond Park on Friday night, with former Cork City midfielder Shane Duggan — who was sent off in that game — captaining the side.
After a quiet opening, Lehane was close to the opener five minutes after coming on but dragged his follow-up effort wide after Cusack made a great save to deny O’Sullivan.
Lehane had the ball in the net five minutes later when he tapped home O’Sullivan’s header across goal from Billy Dennehy’s cross but it was ruled out for offside, which looked marginal at best.
Cusack then denied Lehane with another great stop before the youngster pounced six minutes before the break, when he glanced home Dave O’Leary’s free-kick.
It was all City then and the excellent O’Sullivan showed a neat touch to tee up Darren Murphy two minutes later but the Ireland U19 international’s piledriver came back off the post from 25 yards, with Cusack beaten all ends up.
Limerick had failed to trouble Mark McNulty in the first half as City bossed the game, and the second half continued in the same vein.
Lehane went close to a second five minutes in when he linked up well with O’Sullivan again but Cusack came to his side’s rescue again with another great stop.
Limerick’s let-off was short-lived however as Samuel Oji, who was given the runaround all night, fouled O’Sullivan in the box from the resulting corner kick and referee Jim McKell pointed to the spot.
Cusack got both hands to Billy Dennehy’s penalty but the ball trickle over the line.
Taylor introduced Garbhan Coughlan and Tony Whitehead as he looked to breathe life into his lacklustre side and centre-back Whitehead was denied by the crossbar in the 70th minute when he got on the end of Shane Tracey’s free-kick as Limerick began to wake from their slumber.
But City made sure of the win in the final nine minutes when Lehane headed home his second from Billy Dennehy’s cross, and two minutes later O’Sullivan got the goal his performance deserved when he headed in another superb Dennehy cross.
l Bray Wanderers beat Shelbourne 5-2 after extra-time at Tolka Park last night. Shane Byrne put Bray 2-0 up but Darren Tinnelly grabbed a double for Shels. An extra-time hat-trick from Jake Kelly won it for Bray.
McNulty; Lenihan, Murray, D Dennehy, Dunleavy; Kearney, O’Leary (G Morrissey 75), Darren Murphy (Kavanagh 60), B Dennehy; Elding (Lehane 20), O’Sullivan.
Cusack; Kelly, Oji (Whitehead 64), Folan, Williams (Costelloe 27); Tracy, Nzuzi, Duggan, Hughes, Rainsford (Coughlan 59); Gaffney.
Referee: J McKell (Clonmel)