The quartet – Alex Gregory, Tom James, Pete Reed and Andrew Triggs-Hodge – finished in 5:58.26, almost a second ahead of their Australian rivals James Chapman, Joshua Dunkley-Smith, Drew Ginn and William Lockwood.
The second semi-final was won by the US contingent, but it will be Australia posing the biggest threat in Saturday’s final.
The Brits have dominated the four’s event since 1996, winning at the last three Olympics, including a rousing come-from-behind win over Australia in Beijing.
“That was a really nice semi. That was what we planned but it’s the final that counts,” said Triggs-Hodge.
James warned the Brits will have to step up their performance in the final when facing their Australian rivals.
“We did a good job in our boat, but I don’t know about what the Aussies did in theirs” he said. “I think we can row better and I think we will have to in the final.”
Shortly after the four came the lightweight double sculls, and Zac Purchase and Mark Hunter secured their place in the final as they clinched victory.
The duo won their semi-final in a time of 6:36.63 ahead of French pair Stany Delayre and Jeremie Azou. Their counterparts in the women’s ranks, Katherine Copeland and Sophie Hosking, eased through their semi-final in fine style too.
The pair came from behind to clinch the first, and the fastest, semi-final in 7.05.90 from world champions Greece who finished over three seconds behind in 7.09.01.
Not earmarked as obvious medal material coming into the games, they are a relatively recent pairing.
“Having been a multiple World Cup and Word Championship medallist it has been my aim to reach the Olympic final, but I didn’t underestimate the task,” Hosking said.
Copeland, evidently delighted with making the final, added: “I was thinking only this morning that I didn’t even know whether I was going to get into the doubles this year and now I’m racing an Olympic final. It’s unbelievable really.”
Thursday’s semi-finals wins mean all 13 British boats have made it through to their finals.