WYCOMBE were unable to stop Charlton securing the League One title and lifting their own relegation doom at The Valley.
But they should have.
They had the chances in both halves to leave with a point at least against Chris Powell's side.
But the Londoners showed why they have been the best side in the division this season by pouncing on a single Marvin McCoy error in the second-half and starting a title-winning party in SE7.
For Wycombe, defeat keeps them three points from safety.
Leyton Orient's win means Walsall are the side in their sights.
But the Saddlers have a far superior goal difference so Wycombe will need to pick up at least four points from Notts County at home and Sheffield Wednesday away in the hope of surviving.
A bumper crowd packed into The Valley to salute their promoted side and the atmosphere was electric before kick-off.
A healthy Wanderers away support more than added their voice in the hope of seeing their team secure a win against the odds.
Both sets of fans were treated to a pulsating first-half with Wycombe more than playing their part in an end-to-end affair.
In fact, they started the brighter with Beavon scuffing a shot wide and Matt Bloomfield drilling his low effort past the post.
Blues boss Gary Waddock said a draw was useless for his team in the build-up to the match and his side were not sitting back in SE7.
Far from it.
Joel Grant, who was playing in behind Beavon up-front, was causing problems and sent an effort over the bar as Blues continued to be wayward with their shooting.
And they were punished on 14 minutes when Charlton took the lead.
It was a disappointing goal to concede with Yann Kermorgant scoring with a superb 30-yard free-kick on 14 minutes with goalkeeper Nikki Bull at full stretch.
The Addicks looked deadly going forward with Wright-Phillips twice forcing smart saves from Bull as they threatened to double their lead.
Fighting for their lives, Wycombe got the goal they deserved on the stroke of half-time.
And it came from Beavon who, moments after seeing a shot well saved by Charlton's Ben Hamer, rose in the box to head in an equaliser and keep Wycombe's hopes alive.
They picked up where they left off in the second-half by matching their top-of-the-table hosts with Beavon testing Hamer from distance with an effort before the Addicks stopper was forced to deny Bloomfield from six yards out.
The Charlton goalkeeper was proving difficult to beat and he denied another low Grant effort on the hour mark after the frontman found some space in the home box.
Determination, fight and quality were all being shown by the men in the light and blue quarters as they pushed for a vital winner.
But instead they were punished for a needless error.
Marvin McCoy dwelled too long on the ball and was robbed of possession. The home side ruthlessly took advantage with Dale Stephens firing in to put the home side back in the lead.
It was a cruel blow to Wanderers and, in many ways, summed up their season.
It was a blow they were unable to recover from as Charlton went on to lift the League One title and Wycombe were left with a real mountain to climb.
CHARLTON: Hamer, Wiggins, Cort, Morrison, Solly, Jackson, Pritchard, Stephens, Wagstaff, Wright-Phillips (Haynes 71), Kermorgrant.
Subs (not used): Sullivan, Taylor, Cook, N'Guessan.
Booked: Wright-Phillips (64 mins).
WANDERERS: Bull, McCoy, Foster, Johnson, Basey (Dunne 85), Eastmond, Lewis, Bloomfield, Grant, Strevens, Beavon.
Subs (not used): Laing, Ainsworth, McClure, McNamee.
Booked: Eastmond (36 mins).