THEO WALCOTT booked Saints an FA Youth Cup quarter-final place with a stunning individual goal at St Mary's.
The Newbury Express is still only 15 and does not sit his GCSEs until the summer, but his electric pace and brilliant volley with his weaker left foot were too much for Arsenal in front of a 3,012 St Mary's crowd.
Walcott played the bulk of the match on the right flank but he switched to the left at the beginning of the second half - and caught the Gunners defence flat-footed in the 47th minute.
A speculative ball over the top was the only invitation he needed to display the turn of pace that has earned him the nickname 'The Flying Machine'.
The England under-17 international then crashed a left-footed volley inside the far post from the corner of the Arsenal penalty area for his 11th goal of the season.
Captain Martin Cranie said: "Theo was different class, he just had too much pace for them, and this is a big relief.
"It was probably the biggest game we could have had at this stage but the boys have a lot of confidence because of how we're doing in the league - there's definitely more to come.
"We didn't get the passing going as well as we might have done, but we believe we can go on and win it now.
"I know a few of the Middlesbrough players that won it last year and it would be great to get the trophy off them."
Walcott was Saints' match-winner but goalkeeper Andrew McNeil was the man-of-the-match for his clean sheet against the Arsenal quartet of strikers Arturo Lupoli and Nicklas Bendtner and wingers Anthony Stokes and Ryan Smith.
The Scotsman produced brilliant first-half saves from Bendtner, Irishman Stokes and Italian hitman Lupoli, who also whipped a 25-yarder against the outside of McNeil's right post.
McNeil produced two more crucial saves after Walcott's goal, denying Bendtner on the hour after the Danish striker had slipped past a Saints defender, and then clawing away a Lupoli 20-yarder in the 78th minute.
Arsenal keeper Mark Howard had denied midfielders Tim Sparv and Lloyd James in the first half and Saints had chances to double their lead - all created on the counter-attack by the pace of wingers Dyer and Walcott.
In the 57th minute Howard palmed away a Walcott right-footer after another example of the youngster's blistering pace.
And Dyer missed a glorious chance to score on the counter when he dispossessed Gunners left-back Mitchell Murphy in the centre circle, before sprinting into the vacant Arsenal half - only to miss his 63rd-minute one-on-one with Howard.
In the closing stages, Walcott chased down what looked like a lost cause after a period of concerted Arsenal pressure, only for Adam Lallana to stab wide, while Dyer saw another chance go begging in the 89th minute.
But Saints held on and are now the overwhelming favourites to lift the FA Youth Cup for the first time.
They were the bookies' favourites to win the competition at 4-1 before beating second favourites Arsenal, and they will hope to have striker David McGoldrick, the club's top scorer at under-18 league level this season, back from his knee injury in time to face West Ham or Leyton Orient.
SAINTS: McNeil, Richards, Rudd, Cranie, Critchell, Walcott, James, Sparv, Dyer, Lallana (Condesso 84), Best.
ARSENAL: Howard, Clohessy, Gilbert, Connolly, Murphy, Stokes, Muamba (Randall 86) Gill, Smith, Bendtner (Simpson 82), Lupoli.
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