St Pauli's French forward #29 Morgan Guilavogui (L) and Bayern Munich's Canadian defender #19 Alphonso Davies vie for the ball during the German first division Bundesliga football match between St Pauli and Bayern Munich in Hamburg. AFP
St Pauli, promoted in the summer, fought hard against their heavily favoured opponents and wanted to avoid a repeat of the 8-1 thrashing handed out last time Bayern visited.
Musiala, who scored the only goal in Wednesday's 1-0 win over Benfica, won the ball near the sideline and dribbled centrally before blasting from just under 30 metres, his shot bouncing in off the crossbar.
The 21-year-old now has scored five in his past four games since returning from a hip injury.
Bayern are now six points clear at the top of the table on 26 points, but RB Leipzig can cut the gap to three with a win in their home match against Borussia Moenchengladbach later on Saturday.
Injury-hit Dortmund suffered yet another setback, losing 3-1 at Mainz after Emre Can was sent off in the 27th minute for a studs-up tackle on Lee Jae-sung.
Normally a midfielder, Dortmund's injury crisis had pushed Can into central defence.
His replacement after the red card, another midfielder in Felix Nmecha, was at fault nine minutes later when an unmarked Lee headed in.
Dortmund's Serhou Guirassy won and converted a penalty to level things up but Jonathan Burkardt put Mainz back in front just before half-time, slamming in a Danny da Costa pass from close range.
Paul Nebel added a third early in the second period to put Mainz in the driver's seat for their first home win of the season.
Champions League finalists last season, Dortmund are struggling this year, particularly away from home, having lost their past six games in all competitions.
Bayer Leverkusen's title defence continued to stutter with a 1-1 draw at last-placed Bochum, who equalised in the final minute.
Leverkusen were ahead from the 18th minute onwards after Florian Wirtz slid a ball across the turf and into the path of Patrik Schick, who blasted home.
The visitors seemed on track for victory until Bochum's Koji Miyoshi popped up to grab a loose ball after a mistake from Jonathan Tah and slide it in at the near post.
Leverkusen are now nine points behind Bayern and have dropped 13 points this campaign, more than they did across all 34 games last season.
The draw was just Bochum's second point this season after 10 games in their first match under veteran coach Dieter Hecking.
Elsewhere, Werder Bremen won 2-1 at home against Holstein Kiel thanks to an 89th-minute goal from Oliver Burke after Phil Harres' second-half strike cancelled out Jens Stage's opener for the hosts just after the half-hour.
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)
Short link: