Max Verstappen rounded off the top three after being two tenths off the pace. Let's hope we have the same trust as in Baku where I could get everything out of the auto when I had to.
Vettel and Ferrari team-mate Kimi Raikkonen are driving vehicles showing significant signs of improvement already this season.
"Everything we bring to the track is delivering the expectations and the lap times we were expecting from them", Alonso said. "We can still work on the auto and we should be stronger tomorrow".
Hamilton arrived in Barcelona non-plussed by the four-point championship lead he inherited courtesy of the chaos inherent in racing around the streets of the Azerbaijan capital, Baku.
"Since the last race I have not thought for one second that I am leading the world championship. We have been capitalising on circumstances like the outcome of the last race (in Baku), so I will take it for now but in the long term, the team can not rely on that". "You know we come here over the winter with very cold temperatures and then in May you need to re-adapt a little bit, so it's always challenging".
Robert Kubica was also back competing at his first grand prix weekend in more than seven years after suffering career-changing injuries to his right arm in a rally crash.
The team had to make some modifications to Kubica's vehicle because the Polish driver doesn't have full movement of his right hand.
The virtual safety auto was deployed in the morning when Ricciardo's vehicle ran across the gravel and into the barriers.
The Q1 session began in mild conditions with rain threatening and soon produced drama. "I think it could be a lot more fun", he added.
Stroll almost hit the tyre barriers after going off the track with about a half-hour left in the first session.
It was Hamilton's first victory of a season during which his team have struggled to optimise his auto and tyre performance at every race except the season opener in Australia. "These conditions make it very hard to define where the setup needs to go".
The longest gap between victories in Formula One history was set by Italian Riccardo Patrese, who went 99 races between his 1983 South African victory and 1990 San Marino triumph for Williams at Imola. Raikkonen was sixth, despite the power issue, with Stoffel Vandoorne ninth in his McLaren and Sergio Perez rounding out the top ten in his Force India.