The Spaniard was fastest in the first phase of a rain-hit qualifying and second in the next but suffered when it mattered most after being caught out when the track dried towards the end of the final session.
"The timing was not right, that was very obvious," the double world champion said. "You need to be lucky."
"I think we felt a little bit more competitive today compared to the last qualifyings in July," Alonso, who was critical of his car's performance after the race in Hungary in July, told reporters.
"Here, Monza and Singapore will tell us how much progress we did but it is very positive and a good sign that in the first of these important three races we saw Ferrari fighting for the top positions in Q1 and Q2.
"I'm sure that tomorrow after what we saw today, in whatever conditions we have, if we can pass the people in front it seems that we have the pace to challenge for some good positions."
Alonso failed to score in Belgium last year after being shunted out by Romain Grosjean's Lotus at the first corner in what turned out to be a hammer blow to his championship challenge.
He had been 40 points clear in the standings and on course to chalk up his 24th successive scoring finish. Alonso ended up second at the end of the season, three points behind Red Bull's Sebastian Vettel.
This time, the Ferrari driver is 39 points adrift of Vettel with nine races to go.
However, Alonso said that the lower grid position could turn out to be a blessing in disguise if anything similar happened again.
"It will be more of a problem for those who start fourth, third, second," he said. "I start ninth so maybe I can take it a little bit more easy and gain the positions that the people gained last year with our accident.
"Hopefully there is no accident tomorrow and we have a clean race and we can use our potential. The first corner here is extremely tight, there is always some contact and some front nose that is flying away.
"We need to pass the first lap clean and then use the car."
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