Botman headed home from a Bruno Guimarães corner at the Gallowgate End to nudge Eddie Howe’s side ahead after 24 minutes, but Janelt equalised for Brentford in the 37th minute then Igor Thiago converted from the penalty spot in first-half stoppage time.
The Magpies are seeking a first Premier League win since the dramatic 4-3 victory over Leeds United against a Bees side who have won four of their previous six in all competitions.
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Harvey Barnes let fly inside three minutes but his effort was narrowly wide, then Sandro Tonali was off target from a free kick after Lewis Hall was fouled on the edge of the penalty area.
In the 15th minute, a Tonali corner was punched away by Caoimhin Kelleher as far as Jacob Murphy. His low drive was flicked goalwards by Barnes, but it went the wrong side of the post.
Then Mathias Jensen took advantage of a loose Murphy pass to stride towards the United box but Nick Pope held his 20-yard strike.
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But midway through the half, Botman opened the scoring. It was his third goal for the club and his first at St. James’ Park as he celebrated a century of appearances in black and white.
Jensen had another opportunity for the visitors before superb play from Lewis Hall, with a bursting run and low cross, set up Yoane Wissa against his former club, but his shot was kneed off the line by Janelt.
And the German went on to head home from a brilliant Dango Ouattara ball to equalise for his side.
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Ouattara then cut the ball back for Jensen, whose shot was blocked by Murphy’s arm from close range. The Newcastle man was unfortunate, and it look a lengthy VAR check to ascertain that it was indeed a handball, but Igor Thiago sent Pope the wrong way.
Guimarães returned to the team having missed the last four matches with an ankle injury sustained in the Champions League win over PSG – with United failing to win any of the games in his absence.
Newcastle United: Nick Pope, Kieran Trippier, Lewis Hall, Sven Botman, Sandro Tonali, Yoane Wissa, Harvey Barnes, Malick Thiaw, Jacob Murphy, Joe Willock, Bruno Guimarães (c)
Subs not used: Aaron Ramsdale, William Osula, Anthony Elanga, Nick Woltemade, Dan Burn, Alex Murphy, Jacob Ramsey, Leo Shahar, Sean Neave