He substituted first-choice keeper Paul Smith in stoppage time just before the end of a thrilling 3-3 draw and sent on young penalty-saving specialist Dan Bentley. Smith was furious and stormed off down the tunnel but Bentley emerged the hero, saving from Alfie Potter in the 5-3 shoot-out success to send Southend through in dramatic circumstances.
They will now face Leyton Orient in the two-legged final. Bentley had proved his prowess from 12 yards in the FA Cup second-round replay against Bury at Roots Hall this season with a hat-trick of spot-kick saves.
Sturrock defended his surprise decision to substitute his number one keeper and said: "I had it in my mind to make a substitution. But maybe I should have told my first-choice keeper beforehand I was going to do it. Maybe I should have marked his card.
"But managers are paid to make decisions and big decisions and I'm sure our supporters are going to be happy we're into the area final.
"In one of the rounds before Ben saved three penalties and I just felt he might do something again. I decided if we have a goalkeeper who is exceptional at saving penalty kicks then we should use him. Yes it could have gone wrong and people could have pointed the finger at me but it all worked out."
Sturrock also believes a furious Smith will calm down in time, saying: "He's a big boy, he'll get over it."
Oxford's assistant manager Mickey Lewis said: "We're very disappointed to go out on penalties, these shoot-outs are always a bit of a lottery. They can go either way and we've won a couple of penalty shoot-outs this year.
"It was a cracking game, really open, and I thought we showed good character to fight back after going 3-2 down. We had a couple missing and gave young Tyrone Marsh his first start here and he scored a good goal."
Barry Corr had struck twice for the Shrimpers, adding to the double he got against Brentford in the FA Cup on Saturday, with Sean Clohessy getting Southend's other goal. Tom Craddock and Sean Rigg got Oxford's goals after Marsh had bagged his first goal as a professional.