A miracle play by Ronaldo Mulitalo has inflicted more pain on Brisbane to secure Cronulla a thrilling 36-26 NRL win at Suncorp Stadium.
The Broncos slipped to their ninth defeat from 10 matches despite a much-improved display on Friday night.
Veteran Darius Boyd revelled in his return to fullback, setting up four tries for the Broncos but his efforts were undone as the Sharks stormed home with three tries in the final 10 minutes.
The highlight play came in the 76th minute when Sharks winger Mulitalo put in a clever kick with the outside of his right foot which landed in Connor Tracey's lap to put the visitors ahead.
Another try to Braden Hamlin-Uele in the 78th minute capped the Sharks comeback as a 26-18 deficit in the 70th minute became a 10 point lead.
It's a sixth win in seven matches for the Sharks, who made light of the absence of Josh Dugan, Jesse Ramien, Matt Moylan, Andrew Fifita and Chad Townsend to claim their first win over the Broncos since 2017.
The defeat was harsh on the Broncos, who had looked good for a much-needed win after doubles to Richard Kennar and Kotoni Staggs had given them an eight-point lead with 10 to play.
Boyd, playing in the No.1 jersey for the first time since round 16 last year, added several key defensive plays to a performance which looked a match-winning one until the 70th minute.
The turning point came when a short drop out by the Sharks was spilled by Tom Dearden and Wade Graham regathered.
Moments later the Sharks had scored through Sione Katoa to spark their comeback.
A deflated Seibold said his team had played well but were made to pay for switching off in the final 10 minutes.
Asked whether he would remain in the coaching role until the end of the season, Seibold said he would not walk away despite the Broncos horror campaign.
"See out the season as coach? Yeah I believe so. I certainly won't be quitting," he said.
"I don't think quitting is an example that this young group needs to see or wants to see.
"We've made some big steps forward in the last two weeks but ultimately we've lost both games, and conceded a lot of points."
Jackson Ferris' NRL debut for the Sharks featured a first-half try, being placed on report for a shoulder charge on Brisbane's Herbie Farnworth and then leaving the match in the second half after injuring his left knee.
Broncos' youngster Dearden was also placed on report for a high shot on Siosifa Talakai early in the second half.
Given the key absences, Sharks coach John Morris was delighted with his team's efforts.
"I just thought it was a marvellous effort," Morris said.
"To come from behind, again, 26-18 down, the boys just didn't lose faith and they just dug in and found a way to come home strong.
"That's a really crucial two points for us."
Brisbane are away against South Sydney next weekend while the fifth-placed Sharks play Parramatta.