Harrington and Orr stand at 12-under-par 132 for a one-shot lead over Ian Poulter, who had a 6-under 66 in the second round to reach 11-under 133.
Ignacio Garrido and Christian L. Nilsson also shot 66s and share fourth place with Ricardo Gonzalez (67) and Jean-Francois Lucquin (69) at 10-under 134.
Harrington went 4 under over his last three holes, capping the stretch with an eagle at the par-4 ninth, where he smashed a 403-yard drive downhill and made a 43-foot putt.
The eagle two capped a stellar round that also saw Harrington make seven birdies and two bogeys.
A member of the European team in next week's Ryder Cup, the Irishman is looking to do what he did before playing in 2004 -- win the week before the clash with the Americans.
'I do tend to play better towards the end of the year,' said Harrington, who claimed the German Masters a week before the Europeans won in 2004.
'But winning the week before the Ryder Cup is just coincidence. It's all about goals and focus. When you see the finishing line you know you've got to run a bit faster.'
Harrington heads to the weekend looking for his first European Tour title since winning the '04 German Masters. He won twice on the PGA TOUR last year.
'The putts have certainly dropped for me on the first two days,' he said, 'and I have made a lot of birdies which is good for the match-play format next week.'
Europe has two other Ryder Cup players in the field this week: Darren Clarke, who is competing for the first time since the death of his wife Heather from cancer on August 13, and Jose Maria Olazabal.
Clarke followed up his stunning 4-under 68 in the opening round with an even-par 72 on Friday, falling from a tie for ninth place into a tie for 35th while remaining at minus-4.
'I have put myself in the position of coming out to play this week and I have played well enough to be in contention,' said Clarke. 'I haven't scored well enough, but I have played well enough. I feel that way anyway. If I wasn't happy with my game then I would certainly say, but I am.'
Olazabal has been steady, shooting rounds of 71 and 70 to move into a tie for 42nd place at 3 under.
Orr, meanwhile, joined Harrington in the lead following a bogey-free round. The Scotsman had four birdies on the front nine, including three straight from the seventh, then added three more on the back, including one at the 18th.
He claimed both of his European Tour wins in 2000, at the British Masters and the Portuguese Open.
'There's a long way to go and a lot of guys in a good position, but if I can produce that kind of quality over the weekend I'll be looking good,' said Orr.
The cut line fell at minus-1 with 77 players making it to the weekend.