"Inside the auto, I was going into turn three and I had a feeling there was an issue with the front-left corner and then from there it wasn't anything that I could have done to avoid the impact", Vettel told reporters.
A number of marshalls and vehicles were seen rushing to help Vettel, who walked his Ferrari back to the pits. Until Sergio Perez in the Racing Point knocked Vettel down to third, Sainz held a one-second margin over the field.
"I think we know what [we as a team] need, but it really matters when we find ourselves in that position again and that's what we're working towards".
"We've been exploring a lot of things since day one and I think the last week has been very productive", he added.
Vettel's crash in the morning at the Circuit de Catalunya was the team's first pre-season setback after looking quick and reliable so far.
"The important stuff to come out of this seven or eight days [is that] I think every time I've been on track the auto has been progressing", he said.
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India then went to the United Nations and put enormous global pressure to secure his release about eight days after his capture. Earlier reports had said that the Indian Air Force pilot of the Mig-21 Bison has not returned after usual sortie.
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Of course it's a very hard place to go against a good side but I think with how we're playing we have a good chance to win. Center back Virgil van Dijk also scored twice, both headers from crosses, after Divock Origi had made it 3-0.
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Danny Burch, who worked for the Yemeni Safer oil company, was abducted in the fall of 2017 in Yemen's capital of Sanaa. There had been reports of his release in January of past year but USA officials said Monday those had been erroneous.
"So overall I'm still positive about the auto and the feeling inside the vehicle".
And it coincided with McLaren's announcement that their former driver, the two-time champion Fernando Alonso, was staying on board as a technical adviser and ambassador.
Sainz used the second-softest tyre compound to do his fastest lap, while Vettel was on the harder and slower middle compound as he went about a second slower.
So, he may not be gunning for the title in 2019 - but Sainz at least confirmed that he was happy with both his and new team McLaren's work so far during pre-season testing.
"There are a couple of areas they need to revise and keep developing to improve performance, some others are surprisingly good", Alonso said.
After a power-unit problem kept Mercedes in the garage for the majority of Tuesday afternoon, the world champions made up for lost time on Wednesday with a total of 176 laps between the two drivers. "It is not flawless yet but the direction seems the right one".
There are two remaining days of testing this week, before the season-opening Australian Grand Prix in Melbourne on 14-16 March.