Plea netted half of Gladbach's goals as it won 6-0 in Kiev against a Shakhtar team who had defeated Real Madrid and held Inter to lead Group B after two games.
The Ukrainian side was brought crashing back down to earth in a brutal first half as Plea scored twice, once either side of Valerii Bondar's own goal and before Ramy Bensebaini added the fourth.
Gladbach became the first away side to score at least four times in the first half of a Champions League match since Real Madrid routed Viktoria Plzen 5-0 in November 2018.
Plea's second goal was the pick of the bunch, but further personal achievements were still to come.
The former Nice forward created the fifth goal for Lars Stindl and became the first player to supply an assist in each of his first three Champions League appearances since Opta records began in 2003-2004.
There was still time for his hat-trick strike, too, as Plea benefited from a VAR review after an errant offside call to net the 12th treble scored by a French player in the competition, with only Brazilians contributing more (18).
The final scoreline gave Gladbach their biggest win in any European away match since a 7-0 success against Iceland's IBV in the Cup Winners' Cup in 1973.
It was also Shakhtar's largest European home defeat, although the team now play in Kiev rather than their home Donbass region.