After a goalless first half, on-fire Defoe followed up his double for England against Holland and a midweek hat-trick at Hull City, with a sixth goal of the season that wiped out Carlton Cole's opener, before Lennon secured victory with 11 minutes remaining.
Former West Ham manager Redknapp - who has won five out of five matches on his return to Upton Park - had made two changes from the side that had gone to the top of the table in midweek with that fantastic 5-1 win at the KC Stadium, as keeper Carlo Cudicini and skipper Ledley King came in for Heurelho Gomes (groin) and Alan Hutton.
And in the opening exchanges of this sun-drenched London derby, those sizzling Spurs looked determined to maintain their 100 per cent start as West Ham found themselves battling to contain the pacy and purposeful visitors, who forced a string of early corners.
Gianfranco Zola had also made a couple of changes from the side that won 2-0 at Wolverhampton Wanderers on the opening day of the season as Junior Stanislas and Jonathan Spector replaced the injured Kieron Dyer (leg strain) and Herita Ilunga (fractured jaw).
And on the quarter-hour mark, Cole carved out the first tangible chance of the afternoon, when he volleyed over from 20 yards.
Scott Parker then forced Cudicini into a full-length stop with an awkward low shot from double that distance, before the breaking Cole also found himself frustrated by the advancing Spurs keeper.
But still it was Tottenham, who looked the most likely to break the deadlock and, after Tom Huddlestone's crisp 20-yarder was held by Robert Green, Ledley King headed Luca Modric's well-flighted corner onto his left-hand angle, before the Croatian craftsman drilled an angled shot of his own just inches beyond the far post.
As half-time approached, though, Zola's side came within a stud of taking an interval lead, when Stanislas skipped past Vedran Corluka before crossing into the goalmouth, where Cole agonisingly just could not make contact, to the bewilderment of the short-sleeved Hammers fans among the crowd of 33,095.
Four minutes after the restart, however, Cole well and truly got a full boot to the ball, when he spun King and let fly with a spectacular 20-yard volley that flew past Cudicini to send those home supporters wild.
The casual Cole quickly went from hero to zero, though, as, on 54 minutes, he inexplicably passed backwards from the halfway line and the deadly Defoe gratefully accepted the surprise gift, as he held off Matthew Upson before smashing an unstoppable 15-yarder through the helplessly exposed Green.
Then, with 11 minutes remaining, the overlapping Lennon secured all three points, when he raced onto Corluka's throughball and drilled a low, angled 18-yard winner into the far corner, as the challenging Spector lost his footing at the vital moment.