Alex Mitchell said his surprise call-up as scrum-half for England's crucial World Cup opener against Argentina in Marseille on Saturday had been a "rollercoaster" after missing out on the initial squad.
Mitchell won just his sixth cap in England's final warm-up match last month, when they lost 30-22 to Fiji for the first time.
The Northampton scrum-half's performance, however, was enough to convince coach Steve Borthwick that he deserved a starting spot ahead of veterans Ben Youngs and Danny Care.
Indeed, Mitchell had actually missed out on the initial 33-man squad, with Jack Van Poortvliet preferred as the third No 9.
Van Poortvliet was a late injury withdrawal, however, opening the way for a call-up for the 26-year-old Mitchell.
"It's been a bit of a rollercoaster, out of the squad and now back in and getting a shot tomorrow, I'm just massively excited," he said, adding that Borthwick's decision to omit him from the initial squad had not been badly communicated.
"It was a pretty positive conversation, 'you're not far off', there's a lot of competition in my position."
Mitchell said he was told to "still work on my game, still stay fit because anything can happen and be ready. That's what I did, I stayed fit and stayed ready and got the call to come in and trained hard".
England assistant coach Richard Wigglesworth, himself a former scrum-half who won 33 England caps and was a key player in Saracens European and domestic success, said Mitchell had very good basics.
Mitchell has "an incredibly accurate, quick pass and a good box-kick".
Wigglesworth praised his "speed of service and speed of foot... he's always alive to opportunities".
Mitchell insisted he would not be straying too far off the England gameplan.
"I've got to try and control the game, get the team to tick, when I can create some tempo and energy for the side I'll try to do that," he said.
Wigglesworth added that there was no increased weight of expectation on England going into the crunch Argentina game following their poor run of results, which culminated in that Twickenham loss to Fiji, a fifth defeat in their last six games.
"We're not too interested in expectations outside the squad, to be honest," he said. "It makes no difference to us.
"The squad is incredibly tight and determined. We don’t want to hold back."
Wigglesworth said the team would run out at Stade Velodrome having been told to have a "smile on your face. Go out there and enjoy it, put your game on the field.
"They've been incredibly impressive, excited and ready to go."
England lock Maro Itoje echoed those emotions, saying: "There's a strong feeling and a strong belief within the group that things can change very quickly. The best is yet to come.
"We want to have a great performance for him, for the team, for ourselves, for the country. We're very proud to play for England. We don't take that responsibility lightly.
"We want to be a part of something special."
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