The pair took full advantage of the calm afternoon conditions to card eight birdies without dropping a shot.
It left the duo - polar opposites in terms of European Tour experience - a shot clear of Wales' Stuart Manley and Norwegian Eirik Tage Johansen, the latter's round all the more impressive as it came during strong breezes and sporadic heavy showers in the morning at Penha Longa Golf Club on the Estoril coast.
McGrane had already picked up three shots when he reached the turn but he put the burners on down the back nine - making three gains in a row from the 11th.
And the 2008 Volvo China Open winner carded two more birdies at the 15th and 16th to equal the course record.
“I played solid from start to finish,” said McGrane. “I never really looked like making a bogey all day, and all the time you’re not dropping shots and looking like making birdies, it adds up to a good day’s work.
“It’s all about hitting fairways and greens out there, and giving yourself opportunities, which is what I did. The greens are fairly soft which always makes life easier, and if you manage to roll the ball well on the greens, then you can make a few putts.”
Goddard, a 22 year old from Hendon Golf Club, was part of last year's Walker Cup side but failed to make the cut in his two previous European Tour outings.
But after starting on the tenth tee he eagled his second hole, turned in 32 and birdied his last four holes to match McGrane's bogey-free round.
Goddard, who only got an invite to play on Monday and has his girlfriend Lucy on the bag, said: “I only missed three greens all day, but managed to get it up and down.
“I also holed some nice putts along the way, so it was a good day at the office. I was just plodding along really, but then my round seemed to explode with the four birdies on the trot at the end.”
Manley, who had football trials with Manchester United as a teenager, again demonstrated his best golf on Portuguese soil - he was the halfway leader at the 2008 Portugal Masters before Alvaro Quiros stormed through to take the title over the weekend.
Norwegian Johansen, who has yet to record a top ten finish on The European Tour, produced a sublime round of 65 in windy conditions.
The 28 year old, who has three times graduated from The European Tour Qualifying School, recorded two birdies to reach the turn in 34.
But it was on the back nine that he turned on the style, picking up shots on four consecutive holes from the 11th, adding another at the 16th, then responding to a bogey at the penultimate hole by pitching to three foot on the par five 18th for a sixth gain in eight holes.
"It was really good fun - I enjoyed it," said Johansen. "I was hitting it pretty close on the front nine, then on the back nine I started making some longer putts. So all in all, it was a pretty good day.
"The wind was swirling out there, particularly on some of the more exposed holes. But it's a well-designed course, and it's in great condition.
"The game feels pretty easy at the moment. So I'm just hoping the feeling lasts for the next three days. If it does, I think we're going to have a lot more fun out there. The key to good golf is enjoying it, and I certainly enjoyed myself today."
Two off the pace are England's Richard Bland and Australian Andrew Tampion.
"I hit a lot of fairways and a lot of greens, and more often than not managed to take my chances with some nice putts. You don't get many stress-free days, but that was about as good as it gets," said Bland, looking for his first win in his eighth full season on The European Tour.
Tampion has only made the cut once so far this season, and was relieved by his return to form.
"I've been a bit down over the last few weeks and months, but this week I've come out here with a different thought process after my chat with Nick my sports psychologist, and it seems to have done the trick. I'm enjoying playing golf again, which is great," he said.