Valladolid's win saw them climb out of the drop zone in the Spanish top flight, moving to 16th spot - level with Celta on 15 points and minus-six goal difference.
Guerra took the game away from the visitors on the hour-mark, when he lashed home a right-footed effort from the edge of the area - despite two Celta defenders trying to close him down.
The game's opening goal came just four minutes after Celta were reduced to 10 men, as Brazilian striker Charles was sent off for picking up his second yellow 11 minutes after the interval.
Guerra doubled his match tally when he looped a header from range beyond the reach of Celta goalkeeper Yoel in the 67th minute - a classy finish from a cross in from the left from left-back Carlos Pena.
Oscar then teed up Guerra for his treble late on, with the ball in from the left flicked in by the outside of the striker's right boot to seal Valladolid's third win in 16 matches this season.
The result lifted Valladolid from second-bottom to a two-point buffer on the drop zone.
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