Now, he heads into Sunday's clash against Melbourne entrenched as the Sydney Swans' first-choice centre half-back.
It's amazing what a little confidence can do to turn a footy career on its head.
With Craig Bolton and Lewis Roberts-Thomson out injured, Grundy said he had embraced his new-found responsibility.
"I'm really enjoying it. Obviously I'd like to have Craig and Lewie playing, but Teddy (Richards) played well on the weekend and he filled Lewie's shoes really well," he said.
"You don't get a choice about taking on more responsibility when Craig's not there. It leaves a big hole when he's not playing.
"But playing more games, you get more experience and you spend more time around the boys down there in defence. It's definitely helped."
Grundy's strong hands and his encouraging three-goal debut against Richmond in 2006 gave rise to the thought that he could be the heir to former skipper Barry Hall's key role in attack.
But the South Australian native failed to thrive up forward in the following two years, leading Swans coach Paul Roos to trial him at the other end of the ground.
He began 2009 in attack to cover the absence of Michael O'Loughlin, but returned to defence in the early rounds and never looked back.
Grundy finished the season in the top 10 of the Bob Skilton Medal, behind winner Ryan O'Keefe, and started 2010 in the same fashion as he finished his breakout year.
The 24-year-old said he was more than happy to spend the rest of his career in defence, having finally found his best position at senior level.
And he's also embraced the attacking ethos of Swans defenders that was best embodied by former full-back Leo Barry, who was equally effective at nullifying an opponent as he was setting up play from the last line.
"If everyone's trying to do that down back, as well as defending, it definitely helps the team compared to if there's only Mal (Nick Malceski) doing it, or Marty (Mattner)," he said.
"With each of us doing it, we keep the opposition on their toes and it makes it a bit easier on everyone else."
After his standout 2009 season, a growing partnership with Roberts-Thomson and more experience of playing on the game's best forwards has fortified Grundy's confidence.
While he is looking forward to the challenge of taking on the likes of Lance Franklin, Matthew Pavlich and Jonathan Brown in the next six weeks, he's not getting ahead of himself.
"When you first play on them, you've got nothing to lose. You can just go out there and give it your best. After that, you know a bit more about them, which definitely helps," Grundy said.
"You normally get to play on most of them a couple times each year but so many of the key forwards can turn it on any time you play them. Anything can happen and you can't take one good game for granted.
"But you always look forward to it. With a few games to go, we'll do our best to be playing well and I'll do my best to try and stop them."
