The Gunners, bidding to preserve their slim hopes of winning the title, cruised into a two-goal lead courtesy of goals from Mesut Ozil and Alexis Sanchez.
However, a quickfire double from Andy Carroll just before half time saw Slaven Bilic's side get back into the clash in stunning fashion. During the break, the Croat removed James Tomkins for Emmanuel Emenike in a formational switch which saw Bilic go with a back three for the second half.
Within seven minutes of the restart, it was 3-2 to the hosts as Michail Antonio, playing right wing-back in the departure of Tomkins, stood up a cross for Carroll to power home his hat-trick, and Lennon admired Bilic's nous.
"They can't handle him. It's a magnificent decision by Bilic to change Tomkins and put Antonio at right back. Antonio can now get forward, Emenike will drift inside," he said on BBC Sport.
"He's taken on Monreal and stood up a beautiful cross to the far post and Andy Carroll does what he does best."
Laurent Koscielny later equalised for the visitors with 20 minutes to go as both sides managed a point which, in truth, does not help either side.
For West Ham, victory was needed if they harboured serious ambitions to qualify for the Champions League, but the two dropped points, coupled with Manchester City's win over West Brom, means that the Irons are five points behind the Sky Blues with six games to go.