Teenage striker Leandro Bacuna gave FC Groningen hope of nudging into the UEFA Europa League by the back door after a potentially crucial second-half strike in a 3-2 defeat at Heracles.
Pieter Huistra's side blew their chance to claim fourth place and automatic qualification on the final day of the regular Eredivisie season when they failed to beat PSV Eindhoven.
But Bacuna's 56th-minute effort will give Groningen hope of overturning the first-leg deficit in the return fixture on Sunday and progressing into the final where a qualifying place will be at stake.
Heracles finished three places and eight places behind Groningen in the table but they stormed into a 2-0 lead inside the first quarter-hour with goals from Samuel Armenteros and Darl Douglas.
Jonas Ivens reduced the deficit on 17 minutes for the visitors, but a second from Armenteros on 56 minutes restored Heracles' two-goal lead.
Bacuna hit back almost immediately for Groningen, who had Maikel Kieftenbeld sent off late on.
In the second semi-final ADO Den Haag claimed a 4-2 first leg win over Roda JC after a lightning start which saw Lex Immers, Frantisek Kubik and Dmitri Bulykin all score for the home side inside the first 23 minutes.
Morten Skuobo's opener for Roda on 27 minutes was cancelled out by Charlton Vicento's fourth for ADO four minutes before the break. But Bulykin's red card on the stroke of half-time hampered the home side and Rihairo Meulens made it 4-2 after 78 minutes.
In the promotion and relegation play-offs, former Leicester and Hearts striker Mark de Vries scored twice as Cambuur pulled off a 2-1 home win over Zwolle, who had finished the regular Eerste Divisie season 18 points better off.
VVV-Venlo, battling to avoid relegation after finishing second bottom of the Eredivisie table, won 2-1 in their first leg at Volendam. Ahmed Musa got the winner for VVV two minutes from time.
Two goals in the last seven minutes from substitute Tim Vincken also gave Excelsior hope of avoiding relegation to the Eerste Divisie as his side clawed out a 3-3 first leg draw at Den Bosch.
Veendam and Helmond Sport also shared six goals with Helmond fighting back from 3-0 half-time deficit after Veendam had Michael de Leeuw sent off on 48 minutes. Helmond substitute Etienne Esajas was also dismissed.
The winners of the two-legged ties between Excelsior and Den Bosch, and Helmond Sport and Veendam, will play off for a place in next season's Eredivisie, as will the winners of VVV-Volendam and Zwolle-Cambuur.