Queensland cycling ace Kaden Groves has been pipped for victory in the opening stage of the Volta a Catalunya, edged out astonishingly on the first stage of the celebrated Spanish tour by one of the sport's brightest new teenage stars.

Matthew Brennan, a power-packed 19-year-old British prospect, proved just too strong for Australia's eight-time grand-tour stage winner in an exhausting and enthralling run-in at the end of a tough, rain-sodden opening 178.6km stage around Sant Feliu de Guixols in the north-east of Spain.

Groves looked set for his first win of the year as he and the 19-year-old Brennan gradually hauled in Tibor Del Grosso, who had made an audacious break on a wet descent away from his Aussie Alpecin-Deceuninck teammate and Brennan two kilometres from home.

It seemed inevitable that if they could catch Del Grosso, Groves would use his strength and finishing prowess in the final metres to take victory.

Yet he couldn't find the zip on the uphill finish to get past the stubborn teenager as they both eclipsed the unfortunate Dutchman in the final 10 metres.

It was a win so unlikely for the Team Visma-Lease a Bike youngster from the north-east of England that Australian cycling great, Robbie McEwen, commentating on TNT, just laughed: "Wow, just wow! That's just incredible what he's just achieved.

"The more I watch that, the more unbelievable that is."

Extraordinarily, Brennan, who only made his pro debut in Australia in January with a second place finish on the first stage of the Tour Down Under, has since gone on to win four races in a row this month in his rookie campaign.

Groves, who may have still been paying the price from his exertions in finishing an excellent fifth in Milan-Sanremo on Saturday, could only shrug of the youngster's breakthrough WorldTour win: "Brennan was super strong, and he rode me out of the wheel.

"Super tough ... I didn't have the best legs, but no excuses, I was beaten fair and square."

The young victor Brennan himself just smiled: "At the end, it was such a tricky situation to manage. I just had to go full gas and I'm so happy it ended up like this.".

The race had a very similar finale to last year's equivalent stage, but on that occasion Australian Nick Schultz managed to stay away after he made the late break and held on for victory.

Alas, it ended more painfully for Del Grosso, who, cruelly, just ran out of steam in the last few metres.

"It was really close and it makes it quite bitter. I tried but I had really s*** legs - it was one of the longest kilometres of my life."