Betis will enter Sunday's contest off the back of a seven-goal thriller against Celtic in the Europa League; Pellegrini's team actually trailed 2-0 in the first half but then scored four unanswered goals to take control of the contest before the Scottish giants netted a third in the final exchanges of the contest.
The Green and Whites enjoyed an impressive 2020-21 campaign, collecting 61 points from their 38 matches, which was enough to finish sixth - their joint-best season at this level of football since 2004-05, and they automatically qualified for the group stages of the Europa League.
Betis are part of Group G alongside Bayer Leverkusen and Ferencvaros, and it will be fascinating to see how far the Spanish outfit can progress in the competition, with Pellegrini needing to balance his squad amid a busy schedule, which will see them play another four games before the end of the month.
The Seville outfit opened their La Liga season with back-to-back draws against Mallorca and Cadiz before suffering a 1-0 defeat to Real Madrid before the international break.
Betis returned to winning ways on September 13, though, as a late goal from Sergio Canales handed them a 2-1 success over Granada, which moved them into ninth spot in the table on five points.
Espanyol, meanwhile, were relegated from La Liga at the end of 2019-20, as they picked up just 25 points from 38 matches during a disastrous campaign, but the club secured an immediate return by winning last season's Segunda Division.
The White and Blues are still waiting for their first victory of the new season, with a total of two points from four matches leaving them in 15th position in the table.
Vicente Moreno's side opened their 2021-22 campaign with back-to-back goalless draws against Osasuna and Villarreal before suffering a 1-0 defeat at Mallorca before the international break.
Espanyol were back in action at home to Atletico Madrid on September 12 and suffered another disappointing result despite an encouraging performance, going down 2-1 at home to the Spanish champions.
The promoted outfit have not actually beaten Betis in the league since October 2017 but two of the last three meetings between the two sides have finished in draws.
The home side are also sweating over the fitness of Juan Miranda, who had to be replaced in the second half of the clash with Celtic on Thursday night.
Alex Moreno is now in line to start at left-back, while Guido Rodriguez, Hector Bellerin, Cristian Tello and Rui Silva are among those who should return, with Pellegrini preparing to shuffle his pack for the return to domestic action.
Head coach Moreno will have been encouraged by his team's performance against Atletico, who scored twice in the final 11 minutes to secure all three points, so a similar side on Sunday is expected.
There could be a change of formation for the White and Blues this weekend, though, with Landry Dimata potentially introduced in the final third of the field alongside Raul de Tomas, which could see Oscar Melendo drop out of midfield.
Real Betis possible starting lineup:
Silva; Bellerin, Pezzella, Ruiz, Moreno; Rodriguez, Canales; Tello, Sanchez, Fekir; Iglesias
Espanyol possible starting lineup:
D Lopez; Gil, Cabrera, Gomez, Pedrosa; Vidal, Morlanes, Darder, Embarba; Dimata, De Tomas
We say: Real Betis 2-1 Espanyol
The quick turnaround following Thursday's Europa League clash makes this a tricky game for Betis, and Espanyol are more than capable of picking up a positive result. Pellegrini's side have been impressive in their last two matches, though, and we are tipping another victory for the Seville outfit here.
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