Alonso finished second quickest following the two Friday practice sessions ahead of the Saudi Arabian Grand Prix, just two-tenths of a second adrift of reigning champion Max Verstappen in his Red Bull.
The performance of the two-time F1 champion further underlined the fact Aston Martin has made significant progress this term after Alonso finished third in the season-opening race in Bahrain a fortnight ago.
Following what Alonso said would be an additional test for all F1 teams in Jeddah given they only had one data set after the sole pre-season test and race were in Bahrain, the 41-year-old is cautious going into qualifying.
“Fridays are not very representative,” said Alonso. “In Bahrain, we were okay, like P1 on Friday, and then we were P5, nearly P6 in qualifying, so you never know until we go to qualifying.
“We tested all that we wanted to test in the car. I think there's still not an ideal balance, so we still need to chase a little bit of grip, but so far, so good. It's a good start.”
Free practice hard to read – Alonso
As for the rest of the field, Ferrari, Mercedes and Alpine were all left trailing, adding value to the fact it will be Aston Martin – and Alonso, in particular – that will be challenging Red Bull in qualifying.
Asked, though, if Aston Martin had the second-fastest car behind Red Bull, he replied: “I have no idea. I just drive the car and in qualifying, I'll see where I am.
“Obviously there is a lot of free practice, a lot of days between races, a lot of data to analyse, and a lot of predictions and estimations for you guys to do.
“So that's the beauty of Formula One as well, but for us teams or drivers it is difficult to read anything on free practices.”