Adam Hinshelwood admitted he was "really disappointed" as his side failed to reach the Bostik Premier Division Play-offs after a final day loss to Merstham.
A Kershaney Samuels' strike and Walter Figueira double gave the Moatsiders a three-goal lead inside the first six minutes before Ollie Pearce pegged one back for the home side.
Tom Kavanagh restored Merstham's three-goal advantage from the spot, leaving Worthing helpless to claim the final play-off place, despite Jesse Starkey pulling another back for the hosts.
With their Surrey opponents jumping into the play-offs instead, Hinshelwood felt it was a lost opportunity. He said: "I'm really disappointed to be honest. We played four of the teams that finished above us in the league in our last five games so maybe it's shown we're not quite there yet.
"It was in our hands and we were on a good run. I don't think we took anything for granted but, in hindsight, if we played those five games again maybe we would do things a little bit different."
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Samuels opened the scoring in a crazy opening six-minute spell when he latched on to a misplaced pass from Worthing stopper Lucas Cavagnari before lobbing the keeper from 30-yards out.
Figueira grabbed Merstham's second almost immediately after, unleasing a bending effort past the stricken Cavagnari. The winger then made it three with another curler after outmuscling Aguiar for a second time in as many minutes.
Pearce pulled one back, converting from a tight angle, but Worthing had a further mountain to climb after the break when Aguiar hauled down Figueira inside the box.
With the referee sending off the young midfielder, Kavanagh made no mistake from the spot, smashing the ball past Cavagnari to reestablish the visitors' three-goal lead.
The Mackarel Men cut the deficit again through Starkey's piledriver but were unable to stop their opponents from taking the final play-off place.
Hinshelwood said: "We didn't start particularly well. Going three-nil down after seven minutes makes for a hard afternoon but it's such a shame because for the rest of the game I thought we did really well.
"We all knew the conditions before the game and obviously it's a big factor but we can't use it as an excuse because it had been like that all day."