Newcastle registered their first victory of the post-Andy Carroll era.
Lovenkrands opened the scoring after four minutes and then Best struck early in the second period to wrap up the points for the Magpies.
Birmingham enjoyed a fair share of possession but lacked a cutting edge as they suffered their first defeat in six games.
Newcastle had picked up only two points from three games since Carroll's £35million departure to Liverpool on the final day of the January transfer window.
But they looked the more threatening throughout the 90 minutes, with Jose Enrique surging forward from left-back to good effect. They were well marshalled in midfield from skipper Kevin Nolan and were a constant threat on the counter-attack.
Nikola Zigic, who had scored in the previous three games, posed the biggest threat for the home side.
Newcastle got off to a dream start in the rainswept conditions with Lovenkrands putting them ahead after only two minutes.
Enrique's original cross was cleared after he had skipped past Sebastian Larsson but Jonas Gutierrez pounced on the loose ball and delivered a testing low centre to the near post.
Lovenkrands was first to react and he slid in front of Roger Johnson and drilled his shot past Ben Foster. It was his fourth goal of the campaign.
Blues looked shaky and more good play by Enrique found skipper Nolan inside the box but he did not extend Foster.
Former Newcastle striker Obafemi Martins showed good skill to get past Mike Williamson but Steve Harper was alert to the situation.
Birmingham were now in the ascendancy possession-wise and Johnson headed just wide from Larsson's free-kick
Then Harper did well to turn aside Zigic's shot on the turn from inside the box after good play by Barry Ferguson.
Nolan became the first player to be yellow carded for bringing down Bentley in full flight after 36 minutes.
Midfielder Craig Gardner came close to equalising five minutes before the interval. The midfielder hammered a 20-yard drive just wide after being teed up by Larsson who cut into the box before pulling the ball back.
Newcastle doubled their lead four minutes into the second half through Best's fifth goal of the campaign as Birmingham were again caught cold.
Gutierrez delivered a left-wing cross to the far post and Best got above the normally-dependable Johnson to head home.
Barton was yellow-carded for a challenge on Liam Ridgewell.
Larsson made a crucial challenge to deny Best a second goal after good play by Cheik Tiote
Magpies boss Alan Pardew brought on Nile Ranger for the limping Lovenkrands after 65 minutes.
Johnson was well wide with an acrobatic effort while at the other end Foster gathered a rising drive from Tiote.
Zigic had a great chance to reduce the arrears but headed over from Ridgewell's pinpoint cross when unmarked.
Johnson forced Harper to save his low header from Bentley's centre and substitute Kevin Phillips miskicked inside the box when well placed.
But Birmingham seldom threatened to salvage anything tangible from the game.