They had a pretty rough start but managed to grow into the game and became consistent in their performance. I could remember how they nearly lost to Chelsea in their first game but ended d match as a draw, played a few more games with Bournemouth and Newcastle which they managed to win but wasn’t good performance though. They had this average performance going on for a while and still managed to win matches, no one saw them coming because they don’t play well and gradually they got to top 4 and were just some points behind Arsenal until Arsenal dropped points and they took the top spot.
I don't sure with Chelsea performance in this season will get Champion League spot standings because their performance inconsistency and unpredictable result against mediocre teams with losses many points. Current points left with Arsenal on the fourth standings is 12 points and its not easy for Chelsea if can return to consistent performance. Have two consecutives winning matches in Premier League can't guarantee with promising performance for Chelsea on upcoming match Fulham exactly busy schedule match have to play on FA Cup 3rd round against Preston and few days later will face Middlesbrough on EFL Cup semifinal first leg.
Pochettino must make rotation on upcoming two matches because if push main players have to play on first minutes will make them loss opportunity in domestic league.
Seeing Chelsea's uncertain performance, it is only natural that many people doubt that Chelsea can reach the top 4 and get a ticket to play in the Champions League because their condition is worse than the current top 4.
Moreover, Chelsea is already quite far behind from the top 4 while in terms of getting a spot in the European league Chelsea has to get past 5 clubs and Chelsea has to chase 11 points without losing if Chelsea still achieves a draw and loses then it is certain that Chelsea will probably end up like last season where they didn't get any tickets, either UCL or UEL tickets.
Chelsea has a busy schedule in week 21 because they have to go through 2 matches before meeting Fulham so at least Pochettino has to think about the right strategy so that his players don't lose stamina when facing match in the domestic league and it is indeed better for Pochettino to secure several important players for the match against Fulham Chelsea can playing optimally.