The ex-Magpies and England captain answered an SOS call from his flailing hometown club on Wednesday, but Frank Lampard and Florent Malouda ensured his eight-game managerial tenure opened in defeat in front of a disappointed 52,000 sell-out.
With Joe Kinnear convalescing from a triple heart bypass, Shearer, the top goalscorer in Newcastle history, arrived at the club's Benton training ground on Thursday morning preaching the benefits of man management and rebuilding confidence.
And his impact was evident from the first blast of referee Rob Styles' whistle, but Chelsea silenced supporters in a tight opening half and took the lead 11 minutes after the interval when Lampard headed in following an error from Fabricio Coloccini.
Chelsea arrived with eyes still on the title and Guus Hiddink's side reinforced their aspirations in the 65th minute as Malouda latched onto a pass from the excellent Lampard to slot a second for the visitors.
Replays demonstrated that Newcastle should have had a consolation when a deflected Michael Owen effort was cleared from behind the line by Ashley Cole with 15 minutes remaining as the Tyneside party ended in disappointment.
Newcastle now have just seven games in which to save themselves from relegation, the first of them at fellow strugglers Stoke next weekend.
The Magpies knew they would struggle to match Hiddink's men for innate skill and fluency, and decided to make up for that with effort and sheer bloody-mindedness.
RuggedNicky Butt set the tone with a rugged early challenge on Michael Essien, and Jonas Gutierrez was fortunate to escape punishment for a two-footed lunge at John Terry which drew extended protests from the Blues skipper.
Chelsea rarely sidestep a battle and a tense encounter unfolded with the visitors pressing repeatedly, but meeting stern resistance and Newcastle attempting to hit them on the break.
Clear chances were few and far between, with Steve Harper having to pull off a fine 19th-minute save to keep out Salomon Kalou's diving header and Habib Beye just getting a touch to divert Nicolas Anelka's shot into the side-netting 14 minutes before the break.
The Magpies created only one real opening when Obafemi Martins, perhaps surprised that Jose Enrique's low cross had been allowed to reach him, stabbed just wide of the post with his knee as he reacted late.
But for Shearer, who spent much of the first 45 minutes of his reign stalking the technical area and barking out orders, there was much with which to be pleased.
However, he will have been concerned with the lack of quality of delivery from his wide men, and in particular with Ryan Taylor's inability to avoid the first man from a series of free-kicks in promising areas.
Owen and Martins combined to almost open Chelsea up within three minutes of the restart, but the visitors responded swiftly.
Essien drilled a long-range shot high and wide, but Malouda's clever spin took him in on goal with 51 minutes gone and Harper had to make another excellent block at his near post.
PressureMartins fired wide under pressure from Terry and Alex three minutes later, but the opening goal came with 56 minutes gone, and it went to Chelsea.
Coloccini's dwelled in possession and was robbed by Anelka and, after a poked pass from Lampard, the ball again ran to the Frenchman, who chipped a shot over Harper and onto the woodwork, with Lampard easily heading the rebound into the empty net.
Gutierrez might have done better when he headed substitute Damien Duff's 64th-minute cross straight at Petr Cech, and his side's plight worsened within seconds.
Anelka flicked on Cech's clearance and Lampard slid the ball into the path of Malouda, who despatched a left-foot shot across Harper and into the net.
Owen thought he had pulled a goal back with around 15 minutes remaining when his deflected shot was cleared by Cole, with replays suggesting the ball had crossed the line.
The 29-year-old was in again two minutes later when Martins played him into space inside the box, but his left-foot shot was saved easily by Cech.
But it was the visitors who finished with a flourish as substitutes Michael Ballack and Franco di Santo, Malouda, Kalou and Lampard all went close.
Disappointed applause rang around St James' Park on the final whistle as the home fans trudged away hoping against hope that Shearer could yet be their saviour as Newcastle remain 18th, but fall three points from safety.
1st Half Goals
Shots on Target
Shots off Target