Harrington managed to maintain his overnight lead on the field. At 10-under, the 29-year-old Dubliner is two shots clear of Scotlands Alastair Forsyth (68) and Englands David Gilford (70).
Its pleasing to be in contention no matter where you are playing and Im looking forward to the weekend, said Harrington, who has 13 top-3 finishes in his last two-plus seasons on tour.
While Harrington continued to try and solidify a spot on the 2001 European Ryder Cup team, his playing companion once again faltered.
Colin Montgomerie shot rounds of 72-73-145 to miss the cut. It was the first cut the seven-time Order of Merit champion has missed in Europe since last years BMW International Open.
However, its the second consecutive cut hes missed, dating back to the U.S. Masters Tournament.
Obviously, Im disappointed, said Montgomerie, who last missed back-to-back cuts in 1998 at the Smurfit European Open and BMW International Open.
I had chances coming in but my putting let me down. It is just one of those things but my game is not so good just now. Ill have to go out and work on it and see if I can get out of it. I shouldnt be missing cuts.
Montgomerie is currently 10th on the Ryder Cup standings. Harrington resides in third place.
Gilfords mundane score of 70 belies his roller-coaster round, which featured five bogeys, three birdies and two eagles, both of which came courtesy of holed wedge shots on the par-5 5th and 17th holes.
It was unbelievable. Ive never done that twice in one round, Gilford said. Both shots were pretty identical, about 100 yards to the pin and they just dropped into the hole. I couldnt believe it.
Eighty-two players made the cut, which fell at even-par 144.
Full-field scores from the Algarve Open de Portugal