GREAT Britain sculling star Zac Purchase sent a warning shot across the bows of his single scull rivals at the world championships, going straight through to Thursday's semi-finals in the fastest qualifying time.

The former King's, Worces-ter student took lightweight silver in Japan last year, and wasted no time laying down his credentials for 2006 gold on home water at Eton's Dorney Lake.

The 20-year-old controlled his heat after hitting the front just 250 metres into the race, and cruised home in a time well under the prestigious seven-minute mark.

Greece's Elias Pappas led briefly off the start of Pur-chase's heat, but the River Severn sculler soon forced his bows in front to lead by six feet at the quarter mark with Canada's Jeff Bujas another length back.

His power began to tell in the blustery tail-wind conditions as he moved out to three-quarters of a length at half-way and a length-and-a-half hitting the last 500m.

With the job of securing the sole direct qualifying slot for the semis done, Purchase then eased up in front of the grandstands to cross the line half-a-length in front of Papas in six minutes 56.83 secs.

Bujas was third five lengths back, while the Japanese, Rus-sian and Armenian scullers tailed off.

"I knew I had the race won, so I wound it down a bit," said Purchase, who came back from four months out with a wrist injury to win gold at the Lucerne World Cup regatta last month.

"But I was still under seven minutes and I'm pretty pleased with the way the race went.

"It's a great confidence boost to be the quickest qualifier, but the semis will be tough because everyone will be desperate to get through.

"The Greek guy surprised me a little bit, but I still won with a bit to spare and we'll see if he can challenge again later in the week.

"Conditions were fast, but you've still got to row well to get a quick time and I'm happy with the time and the result."

Of his main rivals, only heat two winner Grant Duncan from New Zealand and second-placed Dutchman Gerard van der Linden, look as though they may challenge Purchase, but they were still four seconds slower than the GB man.