Sainz took over the MCL34 from team-mate Lando Norris, who had finished the first day on Tuesday morning despite two stops on the track, and was fastest on Wednesday morning. He clocked 1: 18.878 minutes at the end of the first hour
His next improvement brought him into the middle of the first M17, before rounding off his lap with a time of 1: 17.144 minutes on the softer C4 terrain sat one hour and a quarter after the session.
That effort was two-tenths faster At the end of the first week of testing last week, Renault Nico Hulkenberg set the 1: 17.393-second set and left Sainz – who also caused the first red flag of the day as he emerged from the pit lane stopped – a full second at the top of the order.
Ferrari driver Vettel was second fastest but was limited to 40 laps by a fall in Turn 3 just over two consecutive laps.
The four-time champion did not improve his personal best for a long time 1
Ferrari said the crash had required a 40-minute shutdown while the car was salvaged and barriers were repositioned, resulting in a mechanical problem. He later added, "We assume the car will not hit the track for a few hours."
The car will be driven in the afternoon by Vettel's teammate Charles Leclerc.
Red Bull's productive start in the second test was continued when Max Verstappen completed 69 laps and set the third fastest time. Once again, the team decided to ride only for the C3 tire.
Valtteri Bottas was restricted to just seven laps on Tuesday afternoon after Mercedes had taken care to change the engine in his W10 due to oil pressure. Finn was doing much better at the beginning of the second day.
Bottas finished fourth with a best time of 1: 18.941 seconds and scored 75 laps, most of the drivers.
Daniil Kvyat's Toro Rosso finished fifth ahead of Alfa Romeo riders Kimi Raikkonen and Sergio Perez of Racing Point. The trio was just 0.142 seconds apart in the middle of the pack.
In the final four minutes of the game, Robert Kubica advanced to eighth place with a lap of 1'19.367 seconds on the C4 tire. who had chosen the harder C2 compound.
Daniel Ricciardo was just under three seconds behind the wheel as Renault concentrated on long runs.
The Australian completed a 10-lap race on the C2 compound early, then drove a 13-lap stint on the C3 tire before the first red flag for Sainz & # 39; stop came.