The Nigerian fired the Magpies into the lead for the first time with 71 minutes gone seconds after replacing Michael Owen, and Lovenkrands sealed victory with four minutes remaining.
Boro took the lead through Habib Beye's third-minute own goal, but Steven Taylor levelled six minutes later after Mark Viduka had hit the post.
Super sub: Substitute Obafemi Martins saves the day for Shearer, striking the winner beyond Boro's Brad Jones just seconds after replacing Michale Owen
Shearer restored Michael Owen to the starting line-up for the must-win derby clash, while Southgate recalled record signing Afonso Alves and handed a first Barclays Premier League start to Marvin Emnes, with Andrew Taylor and Mohamed Shawky also included.
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