Balfour celebrates after her gold-winning swim

The 22-year-old Scot, who just missed out on gold in the 100m breaststroke earlier in the week, finished in a time of two minutes 25.66 seconds.

She led from the start and finished almost three seconds ahead of Ukraine's Yuliya Pidslina in second.

Hungary's Agnes Kovacs was third with another Briton, Kerry Buchan, fourth.

Interview: Kirsty Balfour

Balfour, who swims for the City of Edinburgh club, won a bronze and a silver at the Commonwealth Games earlier this year.

"That's the first gold of the meet and my first gold at a major international," she said. "I was pretty nervous earlier today but I just thought I have to enjoy it and use my talent to swim fast and it worked.

"Although I was number one going into the race I never felt too much pressure. I knew the other girls' best times and I knew Kovacs was off top form so I knew I had a good chance of winning.

"The last 50m was so hard, I'm still feeling the pain from it. I just went out and did what I've practised doing and it worked tonight.

"I'm pleased with the time. It was short of the European record, but that will come."

Mel Marshall and Jo Jackson reached the final of the 200m freestyle after qualifying in fourth and seventh respectively.

Marshall swam a strong race in Hungary

Marshall recorded a time of 1:59.44 while Marshall clocked 1:59.73 in a heat won by Laure Manaudou of France in 1:58.00.

"I'm happy with that," said Marshall. "Tomorrow I've got to do the job against some fast girls. I've got some more to give so I aim to get in there and get the job done."

Stirling's Todd Cooper sneaked into the men's 100m butterfly final in eighth in 53.26.

"That was a pretty messy race from me and I can make it cleaner than that," he said.

James Goddard made the final of the 200m backstroke after qualifying in sixth although Gregor Tait was disqualified from Friday morning's heats for failing to surface before the 15m mark.

James Gibson and Darren Mew both made the final of the 50m breaststroke in times of 28.11 and 28.12.

Italy's Filippo Magnini retained his men's 100m freestyle title ahead of Sweden's Stefan Nystrand.

Dutchman Pieter van den Hoogenband, who has won the event at the last two Olympics but who is returning from back surgery last year, had to settle for bronze.

Russian Yury Prilukov earned his second gold medal of the championships, winning the men's 1,500m freestyle in 14:51.93.

Prilukov, who had already won the 400m freestyle, came home ahead of French duo Sebastien Rouault and Nicolas Rostoucher.