Reading held Chelsea to a 2-2 draw Tuesday after an own-goal by Michael Essien in the 85th minute.
Blues defender Ashley Cole cleared a cross which then deflected off Essien and past goalkeeper Hilario.
Chelsea has 46 points from 20 games, one behind league leader Manchester United which hosts Wigan later Tuesday.
Didier Drogba looked to have given Chelsea the winning goal in the 72nd when he beat goalkeeper Marcus Hahnemann to head in Salomon Kalou's cross for 2-1. It was Drogba's league-leading 12th goal this season and 19th in all competitions.
Earlier, Drogba gave the Blues the lead in the 38th when he outleapt Hahnemann to head in Frank Lampard's corner kick. Forward Leroy Lita headed in a cross for Reading in the 67th to tie it at 1-1.
The game was played without incident after the last meeting between the clubs saw both Chelsea goalkeepers suffer head injuries. Peter Cech is still recovering from a fractured skull sustained in Chelsea's 1-0 win in October, while Carlo Cudicini _ who was on the substitute's bench Tuesday _ suffered a concussion.
Defender Linvoy Primus scored both goals in Portsmouth's 2-1 win at West Ham.
Primus headed in both goals _ off a corner in the 16th and a free kick in the 37th _ to give Portsmouth 35 points, one more than Liverpool which travels to Blackburn later. Teddy Sheringham scored the Hammers' lone goal in the 81st.
At White Hart Lane, Jermaine Defoe scored twice to lead Tottenham to its 12th-straight home victory with a 2-1 win over Aston Villa.
Defoe side-footed a pass from Dimitar Berbatov in the 58th to give Spurs the lead, then doubled the advantage in the 77th.
Captain Gareth Barry scored for Villa three minutes later.
Also Tuesday, it's: Bolton vs. Newcastle; Everton vs. Middlesbrough; Sheffield United vs. Manchester City; and Watford vs. Arsenal.
Charlton hosts Fulham on Wednesday.