Sidwell made his first start for Jose Mourinho's side against his former club while Cech returned to the place where he suffered a fractured skull in the corresponding fixture last season.
However, it was Reading that went ahead in the first-half when a long free-kick was headed back into the six-yard box by Shane Long and although Cech went to punch the ball clear he was hampered by the close attention of Sidwell and Tal Ben Haim as well as Reading striker Kevin Doyle.
When the Czech international completely missed the ball, Andre Bikey, on for an injured Michael Duberry, ran clear to prod it home from close range in the 30th minute.
The double substitution paid dividends, Chelsea equalising within two minutes of the restart.
Both Pizarro and Drogba supplied clever back-headers to a long clearance - and stand-in captain Frank Lampard burst into the penalty area, controlled the ball and beat Hahnemann from close range.
Chelsea then took the lead in the 50th minute through Drogba.
The Ivorian forward played a clever one-two with Kalou, before sending a 20-yard curling effort beyond the Hahnemann for his first goal of the season.