Things didn't look good for West Ham after they were beaten 5-0 at home to Manchester City on the opening weekend of the season.
Now, the Hammers sit fifth in the Premier League, above the likes of Chelsea, Tottenham and Manchester United. Sorry, what?
Well, it's not hard to understand why, under Pellegrini, West Ham are playing some lovely stuff. Free-flowing, quick, direct - the east London club are outplaying most teams they play, going unbeaten in the league since that Man City defeat.
The early signs lean towards this West Ham side being arguably their best of the Premier League era. Physical at the back, pace down the flanks, a fine balance in midfield, creativity in the final third and a top class striker - this team has it all.
After three disappointing campaigns since Dimitri Payet left London Stadium, this may be the season where we see West Ham break into the top six.
Here's 90min's review of September for West Ham.
This could've gone to a whole host of players. Midfielders Mark Noble and Declan Rice were strong candidates, while Aaron Cresswell scored two this month from left-back. The performances of centre-backs Issa Diop and Angelo Ogbonna should also be noted.
However, the hero for the Hammers in recent weeks has been winger Andriy Yarmolenko. After an Achilles tendon rupture ended his debut season in England early, Yarmolenko has bounced back to put in two MOTM worthy displays in September.
The 29-year-old had a major influence in both of his side's goals, scoring the first with a neat turn, roll and finish. Whilst in possession he was able to bring Ryan Fredericks into play down the right and Felipe Anderson on the left with perfect switches of play, we also saw him shut out Bournemouth left-back Diego Rico by tracking his advancing runs side-by-side.
The former Borussia Dortmund man is in a rich vein of form at the moment and West Ham fans will hope it continues.
This was a tough choice, but due to the minimal impact he's had so far, summer signing Pablo Fornals is who we've gone for.
In his three starts this month, Fornals hasn't looked like the confident-self he should be after his stellar season in Spain, which saw him register 17 goals and assists in all competitions.
So far, the former Villarreal man hasn't looked a threat at all in the final third. On occasions he's been afraid to shoot and we haven't seen the creative mastermind that he was in La Liga, averaging 0.7 key passes and 0.6 dribbles a game so far in the Premier League.
Weighing just 67kg, it will take him time to adapt to the physicality of the Premier League and when the creative juices start flowing, there's no doubt that Fornals will improve. The West Ham faithful will just be hoping that they have a player closer to David Silva than Denis Suarez.
Their 2-0 win against United at London Stadium was their only victory of the month and it has to be their best outing.
A Yarmolenko half-volley that put the home side in front rounded off a quiet first half, as West Ham's stout backline kept out a weakened United attack.
The tenacious midfield trio of Declan Rice. Mark Noble and Fornals made life difficult for United's two defensive-midfielders and the visitors struggled trying to link defence to attack. However, in the second period, United looked a little more threatening, with Juan Mata and Harry Maguire spurning golden opportunities.
Nevertheless, Pellegrini's side held their slender advantage going into the final stages and with six minutes of time remaining, Aaron Cresswell secured all three points with a goal we'll talk about shortly.
An impressive 2-0 win for the Hammers, beating United at home for the second season running.
In the league, West Ham failed to put in a bad performance. A 0-0 draw at Villa Park with ten-men was dull, not bad, whilst they dominated Bournemouth for large parts of their 2-2 draw at the Vitality last weekend. With the United victory being the only other league game this month, we're going to have to move over to the Carabao Cup for this one and it's a shocker.
A 4-0 drubbing at the hands of Oxford United, League One Oxford! Fortunately for the Hammers, Spurs' penalty-shootout defeat the night prior meant they almost got away with this one scot-free.
Second-half goals from Elliott Moore, Matt Taylor, Tariqe Fosu and Shandon Baptiste condemned a strong West Ham lineup that included Diop, Fornals and Jack Wilshere to a humiliating third-round elimination.
Aaron Cresswell, you absolute beauty.
1-0 up against United, Cresswell lined up a 25-yard free-kick that was just to the right of David De Gea's goal.
With great technique, pace and trajectory, the left-back whipped the ball over the United wall and perfectly into De Gea's top-left corner. The Spaniard was only good enough to help the ball into the net with his fingertips.
The strike sealed a 2-0 win over the Red Devils and, surprisingly, secured their only victory in September.
With only one win in September and getting embarrassed in the Carabao Cup, it may seem that West Ham have had a poor month.
That hasn't been the case at all and instead, that display at Oxford was a black mark on what has been a very good month.
A point at both Villa Park and the Vitality Stadium are by no means disastrous, whilst their victory against United was mightily impressive.
Pellegrini has this West Ham playing some football you wouldn't typically associate with the Hammers and credit has to go to him for the job he's done. They've built on a decent August and they deserve a good rating for their work in September.
Overall Rating: 8/10