Ireland's own Gary Murphy posted a 5-under 67 to finish one shot off the lead along with Fredrik Andersson, Darren Clarke, Andrew Coltart and Soren Hansen.
Goosen, who is making his first start in Europe since the Volvo PGA Championship, parred his first two holes on the North Course at The Kildare Hotel & Country Club before running off consecutive birdies at three and four.
The South African bogeyed the fifth after an errant drive but countered with a birdie at the very next hole. He added a birdie at the eighth to make the turn at 3-under and kept things going with birdies at the 10th and 13th.
Goosen coasted down the stretch and tallied a birdie at the par-5 last to join Forsyth and Price in the lead.
'To be tied in the lead after the first round is always a healthy position to be in and hopefully I can keep it going,' said Goosen. 'What I have to concentrate on now is getting a good round in tomorrow and then looking forward to the weekend.'
Price got off to a quick start with a birdie at the second and an eagle at the par-5 fourth. He stumbled with a bogey at the fifth but recovered with a birdie at the par-4 seventh.
He collected a pair of birdies starting at the 10th and like Goosen, Price birdied the last for his share of first.
'I picked up an injury and had to pull out of the British Masters,' said Price. 'I've taken a few weeks off so I feel fresh at the moment and ready to go. I finished second here a few years back so it brings back nice memories to come back.'
Forsyth, who needs a strong finish this week in hopes of earning a spot in this month's British Open, was bogey-free on his day and drained a four-foot putt at the par-5 16th for the first of three consecutive birdies to close his round.
'My first year on tour I was very happy but everything went a bit wrong in the second year. I don't know why, maybe my expectations were too high or something,' said Forsyth, who earned his first career victory on the European Tour last season at the Malaysian Open. 'But since then and since Malaysia I have started to play better and better.'
Colin Montgomerie held a share of the lead at one point en route to a 4-under 68. The Scotsman was joined by Mark McNulty and Gary Evans in a tie for ninth.
'I played well,' said Montgomerie. 'I'm driving the ball well, my irons are good and I'm putting much, much better. That's great because I am looking forward to the next three days, I really am, because I think I can win this now.'
Defending champion Michael Campbell of New Zealand had a solid round with four birdies and a double bogey for a round of 2-under 70.