Watford manager Nigel Pearson has backed his players to bounce back after losing in the last minute for the second Premier League game in a row as 10-man Everton left Vicarage Road with all three points.
But Everton would go in at level at the interval as Yerry Mina struck twice in first-half stoppage time and would eventually secure the win late on despite losing Fabian Delph to a red card with 19 minutes remaining.
Watford had been in a good run of form under Pearson before Tyrone Mings hit a 90th-minute winner for Aston Villa last time out, with Walcott repeating the trick on Saturday.
"Exceptionally disappointing," Pearson replied when asked how he judged the afternoon.
"To come in at (half-time) two apiece is very frustrating – We lost it at the death, we had an opportunity to manage the ball better, the game a little better and we didn't – we paid the price for that.
"We have to recover from this, it is never an easy journey when you are in a relegation battle and we have worked exceptionally hard to get back in contact.
"They will deal with it, get on with it and they will have me nudging them and encouraging them in the same way as when we win, they will have the same support now.
"The Villa game was an unlucky late goal and today we have contributed more substantially to our own downfall."
For Everton, this was the first time since December 2017 they have won a Premier League game in which they have conceded the opening goal – a run of 35 games.
They recovered well to the early setbacks as Mina bundled in his first from a corner before heading in the equaliser at the back-post moments later.
They survived with 10 men and were rarely rattled before a three-on-three break saw Richarlison's pass diverted into Walcott's path by Moise Kean's scuffed effort.
The former Arsenal man made no mistake in turning home the winner in front of the Everton support, with manager Carlo Ancelotti pleased to bring such a run to an end.
"I didn't know but this is a good sign, in this moment things are going well," he said when told about the statistic.
"I don't want to be so excited but it is important that we were able to win this really difficult game. It can help us with more positives for the future.
"It was a great and important result also because of what happened in the game."
Asked if he felt like tearing down the touchline with the rest of the Everton bench to celebrate Walcott's winner, Ancelotti added: "I was not able to run, if I run I am dead!"
But he did have a serious response when it was put to him that the win means they are in the pack now chasing European qualification come the end of the campaign.
"No-one knows realistically," he said of what should be the target. "I think we have to try to compete for the top and reach the Europa League for next season.
That would be really important, if we can keep this concentration we can reach the Europa League."