The ice-cool Daniels threw two touchdowns and finished with 299 passing yards and no interceptions as the sixth-seeded Commanders punished an error-strewn Lions performance to leave Detroit's Ford Field in shellshocked silence.
The Lions were one of the most formidable teams of the regular season, their dynamic offence propelling them to a 15-2 record that encouraged many to believe they were ready to win the first Super Bowl in franchise history.
But their championship dreams imploded in spectacular fashion after a litany of blunders - including five turnovers - that allowed Washington to build unstoppable momentum in a gripping slugfest.
Lions quarterback Jared Goff had a nightmare outing, with a costly early fumble leading to a second-quarter Washington touchdown from Brian Robinson Jr. that put the Commanders ahead 10-7.
Soon afterwards, Goff tossed an interception that allowed Washington's Quan Martin to sprint 40 yards into the end zone to give the Commanders a 24-14 lead.
Those scores were part of a frenetic burst of action in the second quarter that saw the two teams combine for an astonishing six touchdowns.
The Lions themselves produced two scintillating moments, with tight end Sam LaPorta snaring a jaw-dropping one-handed touchdown pass, and Jameson Williams racing 61 yards into the end zone after a clever Detroit trick play.
But Washington, led by the nerveless Daniels, always managed to find a response in a contest that at times resembled a heavyweight boxing showdown.
Detroit closed to within three points at 31-28 in the third quarter, but Washington again responded with a Robinson touchdown from one yard out after the Lions helped keep the drive alive with a costly penalty for having too many men on the field.
The game was effectively iced when a risky Detroit trick play saw running back Williams toss an interception, allowing Washington to regain possession and score their sixth touchdown of the night to make it 45-28.
Goff finished a wretched performance with his third interception to end the game in the dying seconds of the fourth quarter.
The Commanders, who finished the season with a 12-5 record, will now face either the Los Angeles Rams or Philadelphia Eagles on the road next week in the NFC Championship game with a place in the Super Bowl at stake.