After beating Linfield 3-0 at the weekend, Ronnie McFall's side were going to prove a handful for the champions, but the visitors will be happy to come away with this fine away win.
The Reds were let off the hook when a Jordan Lyttle header off Casement's just flew over.
Cliftonville created an early chance of their own whenbut Keith got a vital O'Hara blockand David Miskelly followed up with a smart save.
In an action packed first quarter Peter McMahon failed to keep his shot down after being set up by Sean Mackle.
The champions made the most of a defensive mix-up in the home defence to take the lead on 37 minutes, Joe Gormley smashing the ball home after David McDaid, making his debut for the Reds, set him up.
Portadown came storming back and Conor Devlin made two superb saves to keep out efforts from Mark McAllister and Gary Twigg.
However, Tommy Breslin's side held on for the points.
Ballymena were denied victory at Seaview when Timmy Adamson struck a late goal to tie the scores at 2-2 after an entertaining encounter.
Earlier Jordan Owens put the home side ahead on 52 minutes but a superb effort from Gavin Taggart nine minutes later made it one-all.
Johnny Taylor thought he had won it for the Sky Blues when he headed home on 82 minutes, but on a night of late dramas Adamson had the final say two minutes later.
Two second half goals gave Glenavon a deserved 2-0 win at Warrenpoint.
Rhys Marshall and Tiarnan Mulvenna from the penalty spot ensured the three points went to the Lurgan Blues, but they had to work hard at Milltown for the victory.
Eoin Bradley had a great chance to fire the visitors ahead on three minutes but he lashed his shot well wide of the target.
Liam Bagnall went close for Point soon after but his hard shot was well blocked by Conor Dillon.
On 28 minutes Warrenpoint had keeper Parr to thank to keeping them level when he tipped over a goalbound header from Kyle Neill.
Ciaran Gargan tried his luck from 25 yards out but his free kick dipped too late to trouble McGrath in the Glenavon goal.
Glenavon still looked the most likely to score in the second half but they had to wait until 11 minutes from the end to finally beat Parr.
He clipped a great shot over the keeper after latching onto a pass from Martyn.
Warrenpoint conceded a penalty four minutes later when Dermot McVeigh upended Bates and sub Tiarnan Mulvenna swept the ball low and wide of Parr to make it 2-0.
Institute stunned Coleraine at Drumahoe to claim their first win back in the top flight with goals from Stephen Currie and Darren McCauley.
After a scoreless first half the home side forged ahead on 63 minutes Currie curled a superb effort over the keeper Ferry and it got even better for Paul Kee's side ten minutes later as McCauley made it 2-0, firing a low shot into the net.
It was honours even at Stangmore Park as Dungannon Swifts and Ballinamallard settled for a point.
On the half hour mark Dungannon took the lead.
A Ryan Harpur corner was headed back across the goal by Armstrong and Dermot McCaffrey connected with a sweet volley which gave the keeper no chance. Ballinamallard levelled on 56 minutes after Liam McMenamin got on the end of a corner by Anthony Elding.
The Swifts finished the game with ten men after David Armstrong saw red ten minutes from the end.
Wednesday's results in full:
Crusaders 2-2 Ballymena Utd
Crusaders: Owens 52, Adamson 84.
Ballymena Utd: Taggart 61, Taylor 82.
Dungannon Swifts 1-1 Ballinamallard
Dungannon Swifts: McCaffrey 30.
Ballinamallard: McMenamin 56.
Glentoran 2-3 Linfield
Glentoran: Scullion 45, 59.
Linfield: Burns 52, 90, Thompson 72.
Institute 2-0 Coleraine
Institute: Currie 63, McAuley 73.
Portadown 0-1 Cliftonville
Cliftonville: Gormley 35.
Warrenpoint Town 0-2 Glenavon
Glenavon: Marshall 79, Mulvenna 82 (PEN).