The German ace had feared the worst heading into Sunday's Australian Grand Prix after mechanical problems in pre-season testing left Red Bull looking under-prepared for the new season.
But Vettel completed 41 laps in the second session, more than any driver and fourth quickest, while his new team-mate Daniel Ricciardo put in 38 and timed sixth.
Team chief Christian Horner said Friday's workload equated to one-third of the mileage covered in winter testing, a performance that will have eased tensions in the Red Bull garage.
"In the end Friday times are not worth a lot, but it's better to be close to the top rather than somewhere towards the back, so I'm very happy with that.
Also Read
"We will do what we can to prepare for tomorrow and Sunday, but let's see where we are then - the most important thing is that we finish."
Vettel is bidding to emulate Michael Schumacher's five consecutive world titles this season and if he wins on Sunday, he will set a new record of 10 race victories in a row.
"I'm quite surprised today, both Dan (Ricciardo) and I did a lot of laps so that's very good news, so let's see what tomorrow brings," he said. "I learned a lot today, we're in a much happier place already."
Ricciardo, who has replaced fellow Australian Mark Webber at Red Bull, put in a total of 64 laps over the two practice sessions.
"I knew the guys were doing everything they could since testing but still, we didn't expect to do that many laps today, so I'm really happy and pleased for them," Ricciardo said.