The Swiss outfit surprised the paddock when both cars were consistently fast throughout qualifying, with Zhou Guanyu topping Q1 and eventually earning fifth place.
Bottas was as high as fourth in Q2 and then took seventh in Q3, split from his team-mate by the Ferrari of Charles Leclerc.
Alfa has been bringing new parts to the C43 on a regular basis recently, with a major floor package introduced at the last race at the British Grand Prix.
Bottas says he expected the car to be more competitive than it was at Silverstone, where neither driver made it out of the first qualifying segment, but he admitted that he was surprised by the leap up the grid.
“Based on the feeling for the car I did say coming to the weekend that it should feel a bit better than Silverstone,” said the Finn. “But it's much better. I didn't expect that, but we'll take it.
“I think we need to learn something about the new package and the set-up, and the ride heights aren’t optimised, but we're positively surprised how quick we were today, and actually in all different parts seemed to be the case.
“I think this track really brings out the good characteristics. Also normally in the straight line we seem to be a bit draggy, and here's there's only one straight. So less lap time lost there, and it’s quicker on the twisty parts.
Source: Autosport