Sprint star Kaden Groves' team have messed up a golden opportunity at the Giro d'Italia while his fellow Australian speedster Sam Welsford got it absolutely right to win the first stage at the Tour of Hungary.

On a day of contrasting fortunes on European roads for two of the best sprinters in the peloton right now, Groves' Alpecin-Deceuninck team did all the early work to put their in-form man into prime position to take his first stage of the Giro following his runner's-up spot on Tuesday.

But when they needed to push on in the later kilometres of the 178km fifth stage from Genoa to Lucca to chase down a four-man breakaway on Wednesday, they left it too late, along with the other sprinters' teams, allowing French world track champ Benjamin Thomas to snatch the biggest road win of his career.

Thomas sprinted home from Michael Valgren and Andrea Pietrobon to take the fifth-stage honours, while Tadej Pogacar maintained the leader's pink jersey, still 46 seconds clear of Geraint Thomas at the head of the field.

For Groves, though, there was only frustration as Alpecin-Deceuninck had an inquest into how they had controlled the stage from early on, guided Groves to two intermediate sprint wins but, ultimately, miscalculated when trying to chase down the breakaway.

"Yes, it's true (it's a disappointment) but we had a super-strong breakaway," shrugged Groves, who won one stage on the Giro last year.

"We had a plan, we executed the early part really well and unfortunately got a little bit lost in the finale.

"We used a lot of energy early and that cost us a bit in the end trying to bring back the break. I think today the bridge at three-and-a-half kilometres to go really decided the position and I was too far back, and it cost me effectively."

The victorious foursome made their break with 78km remaining but all the sprint teams got the timing of their chase wrong as Thomas, a four-time world champion on the track, cashed in.

"It was like a long, long, long team pursuit," Thomas laughed. "We did an amazing break and I don't believe it. It was really, really hard in the finale, every pull was full gas. It's unbelievable."

Behind the quartet, the peloton closed in too late and were still eight seconds shy at the finish, with Jayco AlUla's Caleb Ewan the leading Australian in sixth place and a despondent Groves eventually coming home 15th.

Meanwhile, on the opening day of the Tour of Hungary, Welsford made up for his disappointment at not being selected by his BORA-hansgrohe team to race at the Giro as he led home a mass sprint at the end of the 166km ride from Karcag to Hajduszoboszlo.

"A perfect stage for Sam," said BORA-hansgrohe's sports director Shane Archbold. "Obviously he's had some fire in his belly with not having the race program he was dreaming of, but it's great to see he turned it around and had a perfect sprint."

Subiaco's former track star Welsford, delighted with his first win since his trio of victories on home ground at the Tour Down Under, said: "In the sprint I had a good position, used other team's trains and had really good legs to take my first win here in Hungary."