"I'm lucky, I'm a natural lightweight," he grins.

But behind his smile there's a secret to his success at Thoroughbred Park.

The Irish-born jockey has been boxing for 20 years and still trains three times a week to compliment his racing duties.

Sweeney will compete in his first group 3 race when he takes Mr Maharaj's saddle in the Black Opal Stakes (1200 metres) at Thoroughbred Park on Sunday.

His boxing training might just give the 35-year-old the edge he needs to topple the industry's leading jockeys.

"It's core strength and fitness, everything you need for racing," Sweeney said.

"You do pretty much everything you need to have top-body strength to push out the horse on race day, so I find it very good.

"I started boxing when I was 15 and gave it up for a while before starting again in 2016. I had my first fight when I was overseas at home and won it. I've been training ever since."

Sweeney rode 17 winners last season and has already equaled that number, with his latest winner being Natalie Jarvis' Fantini at Morya on February 16.

The Todd Smart-train Mr Maharaj finished fifth in last month's Opal Preview (1000 metres) with Sweeney on board, the two-year-old's only start for the stable.

The Canberra-based jockey has ridden the likes of Noble Boy and Gratz Vella's Stephan, but it's Mr Maharaj who now holds a special place in his heart.

"This horse is going to mean a lot to me and for Todd. I've done quite a bit of riding for Todd, he's been very good to me and kept me on," Sweeney said.

"With all the city jockeys coming down he stuck with me and told me I had the ride on the day, so I'm happy with that.

"Having your first ride in a group 3 is where you want to be progressing to, so I'm really stoked.

"It'll be a big day for me but I'm well able to mix with the big boys, it'll be good."

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Five runners in the Black Opal have been nominated for races at Royal Randwick and Flemington but only Ciaron Maher's Muntaseera has been scratched from the $250,000 race so far.

The Freedman-trained On the Lead and Jean Dubois' See You Soon will follow suit, while Cellsabeel will need to pass a vet check due to a sore heel.

Mr Maharaj will start from barrier four in Sunday's Black Opal, a perfect place given the deluge of rain in the capital this week.

"It is a tough race having the horses down from Sydney but with the barrier draw it's good for us," Sweeney said.

"It's a good spot considering the rain we've had in Canberra, being at the rail might be a bit soft.

"I'm thinking barrier four is good come the turn, get out a little bit and then get out going - it'll be better out wide than inside."

Sweeney will also take the saddle of Smart's Our Volantis in the Seppelt Plate (2000 metres), before riding the Vella-trained Mossy Oak in the Riharna Thomson Memorial handicap (1200 metres).

The winning jockey of the Federal race will be awarded the Riharna Thomson bracelet, in honour of the late Canberra track work rider.

He also has two rides on Canberra Cup day with Vella's Willangie in the Lickety Split (1000 metres) and Kerri Kuric's Excitable.

CANBERRA CARNIVAL

Sunday: National Sprint (1400 metres) at 4.30pm, Black Opal Stakes (1200 metres) at 5.10pm.

Monday: Canberra Guineas (1400 metres) at 4.30pm, Canberra Cup (2000 metres) at 5.15pm.