Starting forward, Grimley took only 90 seconds to make an impact, leading out and marking a Bradley Hill pass, before calmly slotting the set shot to join the prestigious 'first kick, first goal' club.
The only thing bigger than the swarm of Hawks players who ran in to congratulate him was the beaming smile stretching across Grimley's face.
"It was the best feeling I've ever had," he told AFL.com.au after the match.
"I'll remember that for the rest of my life."
Grimley's father and grandfather both played for Fitzroy.
Dad Brett played 18 games between 1983 and 1985, and grandfather Ken nine in 1957, kicking half a dozen against Geelong in his first outing.
"He kicked six on debut, but I don't think his first kick was a goal, so I'll always have that over him," Grimley joked.
Despite the strong family pedigree in football, the 199cm Grimley spent more of his teens concentrating on basketball.
He was drafted by Hawthorn after only four TAC Cup games for the Northern Knights and, alongside putting on the necessary bulk to handle AFL football, has also had to learn the intricacies of the native game.
"When I first got to the club I really didn't know much about footy at all," he said.
"I'd played it a little bit, but I didn't know much about it.
"I've come a long way in just learning the different aspects of the game, such as where to run as a forward."
Grimley credited assistant coaches Adam Simpson and Cameron Bruce as major influences on his recent improvement, as well as senior players such as Jarryd Roughead and Jordan Lewis.
After finishing last year in the Box Hill reserves following a mid-season broken finger, his progress has been rapid.
"Last year I was playing development footy and I didn't really know where I was going," Grimley said.
"I broke my finger halfway through the year and had a few weeks off, and came out of that and really attacked the end of the season, and then the pre-season.
"In those last games last year I reckon I had a bit more of a crack, and then over pre-season I just did everything I could to try and get a game in the NAB Cup.
"I was able to play all four NAB Cup games, which was great."
Having now achieved his major 2013 goal of a senior debut, Grimley is hungry for more.
His 14 disposals, seven marks, 11 hit-outs, two tackles and five inside 50s against the Suns – along with that memorable goal – won't have done his chances any harm.
Coach Alastair Clarkson was encouraged by what he saw.
"It was great that he got an opportunity; he's been waiting for a while," Clarkson said.
"He had a really good summer, as he has the last couple.
"We're pleased that he's made significant progress over the last 12 months in particular.
"Hopefully he can play a lot of footy for our club from this point on."
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