Chelsea go second as Liverpool draw again
Liverpool wasted the chance to go level on points with leaders Manchester United after on-loan Egyptian striker Mido converted an 83rd-minute penalty on his debut to earn Wigan a point at the JJB Stadium.
Ivory Coast striker Kalou struck after 58 and 81 minutes to increase Middlesbrough's relegation worries at a rain-lashed Stamford Bridge.
Chelsea have 48 points from 23 matches, two behind Manchester United who thrashed bottom side West Bromwich Albion 5-0 on Tuesday and have played one game fewer than their pursuers.
Liverpool also have 48 points but Rafael Benitez's side have drawn three successive matches and have picked up 11 points from a possible 21 over their last seven matches.
Spain striker Fernando Torres hit the inside of the post with a glancing header early on at Wigan but Liverpool were rewarded for their first-half dominance four minutes before the break when Israeli Yossi Benayoun latched on to a Javier Mascherano pass to score from a tight angle.
But one goal was not enough to claim three points as Mido, who moved from Middlesbrough last week, scored from the spot after Lucas had brought down Jason Koumas.
Benitez described the second half as a "crazy game".
"In a crazy game anything can happen," Benitez told Sky Sports News.
Asked what he was frustrated about, Benitez replied "Everything", before adding without elaborating: "In the second half I was not happy with a lot of things."
The introduction of striker Didier Drogba, again only handed a place on the bench by manager Luiz Felipe Scolari, at the start of the second half provided Chelsea with the attacking impetus to breakdown a resilient Middlesbrough.
Drogba forced Chris Riggott into a rash challenge that earned the defender a booking and soon after the London side broke the deadlock when a corner was only half cleared and Kalou lashed in.
Chelsea's second also came from a corner with an unmarked Kalou steering in Frank Lampard's cross.
Fifth-placed Arsenal's fading title hopes suffered another blow despite Robin van Persie rescuing a point with a last-gasp equaliser in a 1-1 draw at Goodison Park against sixth-placed Everton.
"Our character allowed us to get a point," Arsenal manager Arsene Wenger said after van Persie's goal cancelled out Tim Cahill's fine header.
Britain's most expensive footballer Robinho, arrested earlier this week over allegations of serious sexual assault, played his part in Manchester City's 2-1 win over Newcastle United.
Brazil striker Robinho, who has denied any wrongdoing or criminality, was given a warm reception by City fans at Eastlands and it was his pass that set up Shaun Wright-Phillips for a 17th-minute opener.
Wales striker Craig Bellamy, who joined from West Ham United last week, marked his debut with a second-half goal before Andy Carroll replied for struggling Newcastle who remain just two points above the drop zone.
In other games, West Ham United beat Hull City 2-0 and Blackburn Rovers drew 2-2 at home with Bolton Wanderers.