Sangakkara resumed at Chelmsford on 177, with Surrey 334-7, and had time to bring up his double century before the visitors were all out for 369.
Essex lost Alastair Cook for 36 and fellow opener Nick Browne made 52.
But Dan Lawrence (78 not out) batted through to stumps with Ravi Bopara (33 not out) and saw Essex to 215-3.
Lawrence, 19, and all-rounder Bopara's stand is so far worth 89, but on a decent Chelmsford track the hosts will surely be looking for a big first-innings' lead.
Sri Lanka great Sangakkara, who scored his fifth-successive Championship century on Friday, struck 27 fours in his sublime 321-ball innings and now has 792 runs at an average of more than 113 this summer.
The 39-year-old was the last man to fall in Surrey's innings when he was caught by Neil Wagner off Simon Harmer and was given a standing ovation as he left the field in what will be his final season.
Essex were briefly wobbling at 126-3 in their innings once Tom Westley nicked Sam Curran behind, but Lawrence and Bopara batted throughout the evening session.

Robson-Kanu has not featured for the Championship side since suffering a thigh injury in the 1-1 draw with Cardiff on 19 March.
The 26-year-old featured in eight of Wales' qualifiers but injury ruled him out of the past four international friendlies.
"I'll be fit for the summer," he told BBC Wales Sport.
"I'm getting on well. No-one likes being injured, but it is just a little strain, so I am just managing it now and getting it right, and it will be right come the summer.
"I am definitely on the mend and looking forward to getting back fit."
Robson-Kanu, who is out of contract at the end of the season, expects to feature for Reading before the campaign finishes.
"I will hopefully play a few games and get my fitness up ahead of the camp and as we get ready for the summer," he said.
Wales have qualified their first major tournament since the 1958 World Cup in Sweden and will face Slovakia, England and Russia at the European Championship.
Robson-Kanu believes the success of Chris Coleman's team has helped to challenge the notion Wales is a rugby nation.
"Things have changed, there is this perception that Wales is a rugby nation and of course rugby is a massive part of this nation," he said.
"But if you look at the support Swansea and Cardiff get, especially when Cardiff were in the top league, it was fantastic.
"Now we are doing so well at international level, you can really feel the buzz and the attendances reflect that.
"We know how much it means to the fans, it is that special feeling isn't it? And that is what it is all about."
Robson-Kanu hopes to add to his tally of two international goals in France, and believes Wales can challenge in the tournament.
"What we've achieved getting there, great, but we want to do better than that," he said.
"We have players in the group who are programmed week in and week out to do better than that.
"It will be an exciting summer, but we want to be successful."
Essex's batsman put their side in a good position after Surrey's Kumar Sangakkara fell for exactly 200 on day two of their County Championship match.
[NEXT_CONCEPT]
Reading forward Hal Robson-Kanu says he will be fit for Wales' Euro 2016 campaign in France this summer.