The Reds pair were named in a strong line-up by Roberto Martinez, with the hosts aiming to make it three wins out of three in Group F, which also contains Hungary and Armenia.
Unsurprisingly, Portugal dominated much of the play, as Ireland were restricted to just two shots - neither of them being on target.
Heimir Hallgrimsson's side received plaudits for the way in which they defended resolutely, although Cristiano Ronaldo hit the post and fired wide twice after the break.
The former United man then had a golden opportunity to open the scoring from the spot, when Dara O'Shea was adjudged to have handled in the box 15 minutes from time.