Neither man could match the Australian's pace on the hypersoft tyres, with Vettel 0.229 seconds slower.
The hypersoft compound will be used again at Formula 1's next race, the Canadian Grand Prix, and Ricciardo is confident the Montreal circuit will not produce the same sort of conservative racing.
"We were just cruising around from lap six, maybe", Hamilton said. Kimi Raikkonen, who took pole position a year ago, had to settle for fourth place, just 0.034s off Hamilton and 0.175s clear of the second Mercedes of Valtteri Bottas. The Australian topped the first two stages of qualifying, as teammate Max Verstappen couldn't participate in qualifying after crashing in the practice session earlier in the day, warranting a gearbox change.
That incurred a five-place grid drop, which became academic when the 20-year-old Dutch driver failed to emerge for even one timed lap.
"It feels a little bittersweet". Verstappen will start from the back on Sunday, and could struggle to work his way through the field even in the quickest vehicle: Overtaking at Monaco is notoriously hard.
"This place bites hard if you abuse it. Max is a very fast driver, we know that, and this weekend he has a great auto".
Teams do not want to do more than one pit stop because it means dropping behind other, slower cars, which they can then not overtake no matter how much faster they are.
Daniel Ricciardo claimed victory at the Monaco Grand Prix as he led from start to finish to win the race for the first time in his career. I'm sure that he's smart enough to hopefully learn from that.
Hamilton lost three points to Sebastian Vettel in the Drivers' Championship race, as the German finished in P2 in Monaco.
"He lost the MGU-K 17 or 18 laps into the race".
"I just didn't want to go to risky and have a crash".
"It's still a long race ahead of us tomorrow. I was up a little bit on the last lap but wasn't able to hold on to it", said Hamilton, chasing a hat-trick of wins on Sunday after Azerbaijan and Spain.
Alonso joins fellow F1 champion Lewis Hamilton in openly criticising Sunday's race in Monte Carlo.
Behind the usual suspects, French driver Esteban Ocon qualified sixth for Force India with McLaren's Fernando Alonso, who missed last year's Monaco race to compete in the Indianapolis 500, seventh on the grid.