Jim Irvine added to his already impressive goal tally for the season with a low strike in the 25th minute.
Portadown had several chances to equalize, with Matthew Tipton hitting the post and a Brian Gartland seeing his goalbound effort cleared off the line by Stephen Douglas.
The Ports continued to press in the second half, but Robbie Garrett fired the second goal past David Miskelly in the 81st minute to wrap up a 2-0 win.
The result moves David Jeffrey's side two points clear at the top of the league, and the Blues also have a game in hand.
Elsewhere Glentoran maintained their resurgent form with a 5-0 victory over Dungannon Swifts at Stangmore Park.
Ciaran Martyn opened the scoring with a header in the 16th minute, with Gary Hamilton adding a second in the 49th minute with a fine volley from Stephen Carson.
Carson was again the provider for the Glens' third goal, crossing for Andrew Waterworth to score with his first touch in the 6th minute, and also teed up substitute Darren Boyce in the 84th minute.
Martyn completed the rout with his second goal a minute from time.
In the Belfast derby at Solitude Cliftonville came from behind to secure a 2-1 victory over Crusaders.
Jordan Owens gave the visitors the lead in the 18th minute when he reacted quickest to the rebound from a Declan Caddell effort which struck the bar.
Ex-Crues striker Martin Donnelly hit a superb equaliser in the 33rd minute, with a strike from the edge of the area.
The visitors were reduced to ten men six minutes from time when Gareth McKeown received a second booking, and the Reds capitalised on the extra man when Joe Gormley pounced on a rebound after Donnelly's effort was well saved by Sean O'Neill.
In the game at Seaview Ballymena Utd picked up a valuable away win with a 2-0 result against Carrick Rangers.
Jordan Baker opened the Sky Blues' account in the 50th minute, with Gary McCutcheon netting at the back post ten minutes later.
Glenavon's woes continued as they lost 2-1 to Donegal Celtic despite taking an early lead in the game at Suffolk road.
Conor Hagan put Marty Quinn's men in front with just three minutes on the clock with a fine 18-yard strike, but Darren Murray headed in the equaliser ten minutes after the restart.
The Lurgan Blues lost Ciaran Doherty to a straight red card soon after, and Donnelly popped up to fire home the winner in the 82nd minute.
In the game at Ballyskeagh Coleraine came back from a goal down to beat Lisburn Distillery 2-1.
A poachers goal from Gary Liggett just before the break was cancelled out five minutes into the second half when Whites' goalkeeper Billy Brennan allowed Curtis Allen's shot to run through his legs.
Allen added a second against his former club midway through the second period when he headed in a Ryan McIlmoyle cross, and McIlmoyle got himself on the score sheet with a header four minutes from time.
IFA Carling Premiership results:
Carrick Rangers 0 - 2 Ballymena United
Ballymena: Baker 50, McCutcheon 60.
Cliftonville 2 - 1 Crusaders
Cliftonville: M Donnelly 33, Gormley 90.
Crusaders: Owens 18, McKeown sent off 83.
Donegal Celtic 2 - 1 Glenavon
Donegal Celtic: Murray 56, 82.
Glenavon: Hagan 3, Doherty sent off 62.
Dungannon Swifts 0 - 5 Glentoran
Glentoran: Martyn 16, 90, Hamilton 49, Waterworth 66, Boyce 84.
Linfield 2 - 0 Portadown
Linfield: Ervin 22, Garrett 81.
Lisburn Distillery 1 - 3 Coleraine
Lisburn Distillery: Liggett 42.
Coleraine: Allen 53, 74, McIlmoyle 86.