Receiver Saubert made the decisive two-point conversion for Seattle.
Seattle engineered a remarkable fightback to defeat the Rams in overtime, securing their spot in the postseason.
Rallying from a sixteen-point deficit in the final period, the Seahawks emerged victorious by a single point at home, notching their fifth straight victory.
While the Los Angeles had already secured a playoff spot earlier on Sunday, the Seattle team secured their place to the play-offs after a two-year absence.
With this outcome, the Seattle now lead their division's standings with a 12-3 mark, replacing the Los Angeles, who fell to the number five seed with an eleven and four record.
Quarterback Darnold had two picks but regrouped to make two scoring throws, including the second score to star receiver Jaxon Smith-Njigba in overtime.
The Rams held a six-point advantage at half-time before Kenneth Walker III broke free for a 55-yard scoring dash for Seattle.
Rams defensive back Josh Wallace then took back Darnold's first pick for a big return, setting up a one-yard touchdown by Blake Corum on the ensuing snap.
In the fourth quarter, a touchdown from Stafford to Nacua pushed the Rams' lead to 30-14, but Rashid Shaheed provided Seattle's comeback with a spectacular punt return.
Darnold then found Barner in the end zone, and a converted two-point play sent the game into overtime.
Although Nacua scored for his another TD in overtime, Jaxon Smith-Njigba answered in kind to setup the game-winning conversion.