Suzy Whaley is playing with the men this week and opened with a 5-over-par 75.
Dennis Paulson posted a 6-under 66 to finish one shot off the lead. Craig Barlow was one shot further back at minus-5.
Both Haas and Jacobsen, who at the age of 49 are close to joining the Champions Tour, showed that they still have plenty left in the tank at the TPC at River Highlands.
'As I have gotten older my priorities have changed a little bit,' said Haas. 'I enjoy my time at home more than I used to, I guess. But I think just keep being passionate about the game I think is probably the most important thing for me.'
'Jay and I come out of the same tour school back in '76, so I have been impressed and inspired by his play this year,' Jacobsen said. 'If he wins this week it wouldn't surprise anybody out here as well as he is playing.'
Haas hit his second shot to 10 feet at the first to begin a stretch of three consecutive birdies out of the gate. He rolled in a 15-foot putt for a birdie at the par-5 sixth to make the turn at 4-under.
At the par-4 10th, Haas hit his approach to eight feet and Haas continued to roll with a birdie at the par-3 11th after his tee shot stopped 12 feet from the hole.
Haas then converted a five-foot putt for a birdie at the par-5 13th and had a shot at another short birdie at the 17th but ultimately missed the cup.
'Even though it is playing long, the ball just sticks in the fairway, doesn't run off to the edges too much,' said Haas. 'I think everybody tapered off a little bit and Peter and I kept going.'
Jacobsen, who won this event in 1984, ran off back-to-back birdies from the first to start his round. He hit his tee shot to 20 feet at the par-3 fifth and dropped a 9-iron inside 15 feet for a birdie at the sixth.
At the par-4 ninth, Jacobsen's 9-iron stopped 20 feet from the cup to set up another birdie. Jacobsen sank the putt to make the turn at 5-under and reached minus-6 with a birdie at the 15th.
Jacobsen stumbled with a bogey at the 16th but recovered with a birdie at the 17th and knocked his approach inside two feet for a birdie at the 18th.
'Physical conditioning takes a back seat to mental conditioning. I mean, I can give you a lot of names of kids out here that are in great shape that will never win because you know what I'm saying,' said Jacobsen. 'You can laugh at Stad and say that physical condition is not a factor to him. It may not be a factor, but he knows what's going on in here, and he has it here.'
While Haas and Jacobsen lead the field, the galleries were treated to Whaley's first round on the PGA Tour.
'I think any time a tournament has a special attraction like a Bill Murray or a Suzy Whaley, it's only a good thing,' said Jacobsen. 'I think what Annika did for the PGA Tour and for golf in general at the Colonial was awesome. I think Suzy playing this week, I played nine holes with her on Tuesday, her attitude is fabulous.'
Whaley, who won last year's PGA Connecticut Sectional to earn a spot in the field, got off to a rough start with a double-bogey at the opening hole. She dropped another shot with a bogey at the third but settled down from the point on.
'It was so exciting. There were so many people there yelling for me, cheering for me, supporting me and it was a great moment,' said Whaley. 'I was extremely nervous on the first hole but I kind of got past it as soon as I did my pre-shot routine. I was very nervous on the green but then I settled down and by the second green I really wasn't that nervous anymore.'
Whaley sank a long putt to save par at the sixth before notching a bogey at the seventh. She bogeyed the 10th but picked up another good par save two holes later at the 12th when she rolled in a putt from the fringe.
The 36-year-old club pro then picked up a bogey but closed her round in style with a birdie at the par-4 18th for a round of 75.
Kenny Perry carded a 4-under 66 to join K.J. Choi, Willie Wood, Todd Fischer, Jonathan Kaye and J.J. Henry in a tie for fifth.
Two-time defending champion Phil Mickelson, who has struggled since contending at the Masters, started with a bogey at the 10th, his first. Mickelson then tallied four birdies over his next eight holes to make the turn at 3-under.
Mickelson moved to minus-5 with birdies at the second and the sixth but faltered with back-to-back bogeys starting at the seventh to head to the clubhouse at 3-under-par 67.