They held off a strong challenge from Romania to take the win as Australia came in third.
Great Britain finished fourth, a length behind Australia, to claim the last available place in Thursday's final.
The Great Britain men's Lightweight Four underlined their Olympic gold medal potential with a commanding semi-final victory.
They unleashed a powerful sprint for the line to surge clear of Switzerland in the final 500m.
The British crew won in 5:59.68 seconds, just quicker than the time posted by chief gold medal rivals Denmark in winning the second semi-final.
Elsewhere, the men's Double Scull of Bill Lucas and Sam Townsend finished third in their semi-final behind the Slovenian crew, who were Olympic champions 12 years ago, and Lithuania.
There was a shock in the first heat with reigning Olympic champions Australia and world silver medallists Germany failing to qualify.
I feel in very good form, but I've got to keep a lid on it, I don't want to get too over excited or anything elseAlan Campbell
Alan Campbell moved smoothly into the semi-finals of the Single Sculls with a length victory over Germany's Marcel Hacker to underline further Great Britain podium credentials.
He said: 'I feel in very good form, but I've got to keep a lid on it, I don't want to get too over excited or anything else and when it comes to the final the gloves are off and we'll go out fighting.'
New Zealand's Mahe Drysdale remains the favourite to add Olympic gold to his five world titles and he won the first heat, ahead of Belgium's Tim Maeyens.
Lassi Karonen of Sweden is hitting form at the right time and he won the third quarter-final, while Ondrej Synek won his heat with reigning Olympic champion Olaf Tufte scraping through in third place.