Having turned a session-low 21 laps, Alonso ranted on the radio at one stage that: "The engine feels good". Adding insult to injury, it happened to Fernando Alonso at his home track.
Vettel, a four-times world champion, is 13 points clear of Mercedes' triple title victor Lewis Hamilton after the German won in Australia and Bahrain.
All the data gleaned during preseason testing and all the experience gained during the first four races culminates in a raft of updates installed at the Circuit de Barcelona-Catalunya.
The ambient temperature at the start of the 90-minute session was 66 degrees Fahrenheit (19 degrees Centigrade) and the track temperature was 75 degrees Fahrenheit (24 degrees Centigrade).
Ferrari finished pre-season testing on top, and Hamilton said that while the latest upgrade to the Mercedes was not a game changer, the auto feels significantly different this weekend to how it did at Barcelona two months ago. "I think it's normal that you have races where there's more overtaking and then less", he said. "It's just a bunch of small things can make a big difference".
The 35-year-old Spaniard, yet to finish a grand prix this season and who failed to even start in Russian Federation after an engine issue on the formation lap, suffered an oil leak before grinding to a miserable halt in front of his home fans.
Since debuting at the Spanish Grand Prix in 1977 as Williams Martini Racing, only Ferrari and McLaren can boast more than their tally of 114 wins - although the last of those came in Spain for Pastor Maldonado five years ago. The frustrating times continue for Alonso, Honda and McLaren. Hamilton clocked a 1:20.802 on the soft tyres, purple in the final sector, to top the session.More news: Giant sea creature washes up on Indonesia's Serum Island
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Vettel was the next to strike trouble. The marshals pushed the auto back into the pits to be collected by the Ferrari crew.
But F1 fans would be wise not to jump the gun, because at the Spanish Grand Prix Ferrari faces the sternest test of its title mettle to date.
Watching the progress of Toro Rosso for the remainder of the season will also be intriguing, as they have an up-to-date power unit on hand, unlike in 2016 wen they used year-old Ferrari power.
Hamilton was quickest in the day's second session too, his advantage over Bottas widening by the slenderest of margins.
Bottas's 2014-16 Williams team-mate Massa believes Sebastian Vettel is already clearly established as the sole championship contender at Ferrari, and that this could force Mercedes to put its resources behind Hamilton unless Bottas makes an immediate case for his own title potential. "I struggled a bit with the vehicle balance in general so conditions today seemed to be quite challenging".
Bottas was second, 0.090s down, with Raikkonen was 0.310s off the pace and Vettel a further tenth down.