The visitors have picked up one point from the last 21 and are four points above the dropzone with two games to go, while Betis are merely jostling for position in mid-table.
Betis' season is well and truly petering out, with 12th place now the best they can aim for ahead of games with Alaves and Real Valladolid, and focus has already turned to 2020-21.
Pellegrini has experience of guiding Villarreal and Malaga to the latter stages of the Champions League and has already stated that is his aim with Betis.
That will not be an easy task, of course, with Los Verdiblancos enduring an inconsistent campaign that will end with them seven points off a Europa League spot at best.
Sporting director Alexis Trujillo is tasked with taking charge of Betis' remaining two games and six points will be the target.
Alaves will see this as the perfect fixture for them, though, against opponents who have perhaps taken their eye off the ball, even if they did give Atletico Madrid a run for their money in Saturday's 1-0 loss.
Juan Muniz's men ended a worrying six match losing run with a goalless draw against Getafe at the weekend, and that point may well be enough to keep them above the dotted line.
Leganes and Mallorca are four points worse off in 18th and 19th respectively, but Alaves will want to get the job done on their terms.
Given that they face Barcelona in the final round of fixtures, they will have to pick up a victory at the Estadio Benito Villamarin for that to happen.
Alaves are winless their five last La Liga games against Betis and have not beaten Andalusian opposition in nine attempts since May 2018, however, so they will need to end that run on Thursday or hope that other results go their way.
Real Betis' La Liga form: WLLDWL
Alaves' La Liga form: LLLLLD
Trujillo is expected to stick with Loren Moron up top, meanwhile, with the striker directly involved in 12 goals in 34 league games this term - one fewer than the last two seasons combined.
Alaves are without Martin Aguirregabiria for this trip to Sevilla after the defender was issued with a fifth yellow card of the season against Getafe.
Ximo Navarro is in contention to feature at right-back, then, although he is also carrying an injury.
Real Betis possible starting lineup:
Martin; Emerson, Mandi, Sidnei, Moreno; Rodriguez, Carvalho; Fekir, Canales, Pedraza; Moron
Alaves possible starting lineup:
Jimenez; Navarro, Ely, Laguardia, Marin; Burke, Garcia, Pina, Mendez; Perez, Joselu
We say: Real Betis 1-0 Alaves
Alaves will be looking to put at least another point on the board here, but they have lost their last five away matches without scoring and it is difficult to see that run ending at the Estadio Benito Villamarin, where Betis are unbeaten in nine against Basque opposition.