In what was always going to be a physical contest, the Blues raced to a 22-0 lead after 35 minutes on Saturday and held off a Drua fightback to join the Waikato Chiefs and Wellington Hurricanes in the semi-finals.
The Hurricanes earlier beat the Melbourne Rebels 47-20 in the New Zealand capital to drop the curtain on the 14-year existence of the Australian outfit.
The Chiefs beat the Queensland Reds 43-21 in Hamilton on Friday.
The Blues had missed out on top spot in the final standings only on points difference, while the Drua had not won on the road this year and the gulf in class was clear in the first half at Eden Park.
Flanker Dalton Papali'i, scrum-half Finlay Christie and Clarke crossed for tries as the Blues executed with precision and the Drua made a succession of errors.
Fiji winger Selestino Ravutaumada triggered a Drua fightback with a brilliant, mazy run for a try three minutes into the second half, and for a while the visitors grabbed the momentum.
The Blues never recovered their dominance, but replacement hooker Kurt Eklund scored a try and Clarke scythed through the defence to grab his second to snuff out any hope of an upset.
"I don't think the scoreboard reflects how tough a game that was, they really brought it to us," said Papali'i, who took over as Blues captain when Patrick Tuipulotu went off with a knee injury.
"It's finals footy now, it's the best teams now playing for the end goal, and that's to win the whole thing. Week by week we've got to turn up."
