The Red Rose made it three wins from as many Quilter Nations Series matches last Saturday as they claimed a sensational 33-19 win against New Zealand at Allianz Stadium.
Mitchell started that match, along with Saints team-mates Alex Coles and Fraser Dingwall, who grabbed a second-half try.
And Henry Pollock was also involved as he produced another crucial cameo off the bench, coming on to set up a try for Tom Roebuck.
The victory was England’s first on home soil against the All Blacks since 2012 and their first against New Zealand anywhere since the Rugby World Cup semi-final in 2019.
England, who have not had an autumn clean sweep since 2010, have now beaten the All Blacks, Fiji and Australia this month.
And their final match comes this weekend as Argentina come to town, having just claimed a stunning 33-24 comeback success against Scotland at Scottish Gas Murrayfield last Sunday.
The Pumas were 21-0 down in that encounter, but they roared back, scoring five unanswered tries to win it.
It means this Sunday’s clash at Twickenham will be between two buoyant teams.
And after the victory against the All Blacks, in which England bounced back from going 12-0 down early on, Saints scrum-half Mitchell said: “It was a massive win.
"Hopefully we can go four from four in the autumn series.
"I feel fantastic, the crowd felt extra loud on Saturday, and we found a way to get the win.
"Going 12 points down was always going to be hard to come back from against quality opposition, but we found a way, we dug in and got the result so we are buzzing.
"To have someone like (man of the match) George (Ford) outside me makes the job so easy - he gets in the pocket - puts us in the right positions, and the little things he does that no one sees like talking off the ball is brilliant and his kicking game is fantastic as well.”
England boss Steve Borthwick was delighted with his side’s showing and he explained how Maro Itoje’s team-talk proved key against New Zealand.
“Maro addressed the team on the morning of the game and he talked about when the team were 14, 15 years old,” Borthwick said. "When they were dreaming of playing for England, dreaming of playing here at Allianz Stadium against teams like New Zealand, dreaming of beating teams like New Zealand, here.
“He asked the players to go out and play with that intent that of a 14 or 15 year old, who has the dream, does.
“The boys took those dreams onto the pitch and I thought they were outstanding.
"This is about trying to achieve special moments, special memories. This is one of them.
“Hopefully, there is a load of other young future rugby players watching that game around the country who want to wear the white shirt and get great victories for England in the future.
"Hopefully it is a moment for that.”
