Russian has now lost three straight matches, but there was a better result for Pliskova while over on the ATP Tour, Goffin pulled off a remarkable fightback.
Maria Sharapova extends winless run with first round defeat to Caroline Garcia at Stuttgart Open
Maria Sharapova extended her winless run to three matches after losing 3-6, 7-6, 6-4 to Caroline Garcia in the first round of the Stuttgart Open on Tuesday.
Sharapova, 31, returned to the event where she made her comeback last year from a 15-month doping suspension, but the Russian former world No 1 could not repeat her deep run of 2017 when she reached the semi-finals.
Sharapova, a three-time winner in Stuttgart, raced in to a 3-0 lead and remained impenetrable on serve throughout the first set, dropping just five points.
However, Garcia settled into the match during the second set and earned the first break to lead 4-2. The Frenchwoman's advantage did not last, though, as Sharapova broke straight back. After both women held their remaining service games, it was Garcia who edged the tie-break.
Sharapova then claimed the early lead in the decider, but her 2-0 lead lasted one game as Garcia broke straight back. Once again, both players remained strong on serve, until Garcia claimed the decisive break before serving out the match.
"I think it was a very close match," Garcia, 24, said in her on-court interview. "I know she's a fighter and until the end, it would be very difficult.
"I was more aggressive today and I returned a little bit better. Finally, I can say that after seven years, I beat her."
The defeat means Sharapova has now lost three successive matches following first round defeats at the Qatar Open and Indian Wells.
Karolina Pliskova had a far more straightforward outing, defeating Kiki Bertens of the Netherlands 6-2, 6-2 in exactly one hour. The world No 5 from Czech Republic will take on either Spain's Carla Suarez Navarro or Russian qualifier Veronika Kudermetova in the second round.
World No 1 Simona Halep will begin her Stuttgart campaign on Wednesday when she takes on Magdalena Rybarikova in the second round. Angelique Kerber, Petra Kvitova and Sloane Stephens will also be in action.
On the ATP Tour, Belgium's David Goffin staged a remarkable fightback to beat Spaniard Marcel Granollers-Pujol in the first round of the Barcelona Open.
Goffin, the world No 10, was trailing a set and 1-5 before clawing his way back into the match to win 4-6, 7-6, 6-2.
Malek Jaziri is also through to the second round. The Tunisian world No 88, who reached the semi-finals of the Dubai Duty Free Tennis Championships this year, was a comfortable 6-4, 6-3 winner against American Ernesto Escobedo.
Defending champion Rafael Nadal will begin his bid for an 11th Barcelona Open title on Wednesday when he takes on fellow Spaniard Roberto Carballes Baena. World No 1 Nadal arrives in Catalonia fresh from winning an 11th Monte Carlo Masters title.
Serbia's former world No 1 Novak Djokovic will also be in action when he takes on Slovakian Martin Klizan, while Monte Carlo finalist Kei Nishikori will start his campaign for a third Barcelona title against Spain's Guillermo Garcia-Lopez.
Bulgaria's world No 5 Grigor Dimitrov takes on Gilles Simon in the second round after the Frenchman beat Belarusian Ilya Ivashka 6-2, 6-3 in the first round.