Bailey, 20, gave Leverkusen the lead at the BayArena when he hit the back of the net from 20 metres with a left-footed strike.
There was nothing on when Bailey looked up on the edge of the area, but his shot across goal gave Mainz goalkeeper Robin Zentner no chance three minutes into the second half.
After also scoring last weekend with an audacious backheel, it was his eighth league goal this season.
Leverkusen could ask Chelsea or Arsenal for double the €13.5million they paid Belgian club Genk for Bailey in January 2017.
However, the German side have ruled out selling him in January’s transfer window and the Jamaican is under contract until June 2022.
It was the latest eye-catching display from Bailey who scored and created a goal in last weekend’s 4-1 thrashing of Hoffenheim.
Take a bow, Leon Bailey! pic.twitter.com/BW2uM56hKb
— Footbie (@footbie) January 28, 2018
Leverkusen made sure of the three points against strugglers Mainz when Brazilian left-back Wendell converted a 68th-minute penalty, after Mainz defender Giulio Donati brought down striker Lucas Alario.
The win sees Leverkusen climb to second, 16 points behind runaway league leaders Bayern Munich, who thrashed Hoffenheim 5-2 at home on Saturday.
The Bundesliga’s top-scorer Robert Lewandowski scored for the 18th time in the league this season as Bayern fought back from two goals down in style.
VfB Stuttgart sacked coach Hannes Wolf on Sunday, after Saturday’s 2-0 defeat by third-placed Schalke saw them slip to 15th in the table.
Leverkusen are above Schalke on goal difference, with Eintracht Frankfurt a point behind in fourth.
Borussia Dortmund are sixth after needing a 93rd-minute equaliser by left-back Jeremy Toljan to salvage a 2-2 draw with Freiburg.
Arsenal target Pierre-Emerick Aubameyang produced a poor display and was whistled on his return after being dropped for the previous two games.
Dortmund were whistled by their own fans and Stoeger admitted he was also unimpressed with what he saw.
“I didn’t whistle, but I wasn’t happy,” he quipped.
The Bundesliga‘s growing reputation for attracting raw teenage talent from around the world was reinforced this week when RB Leipzig signed highly-rated 16-year-old Danish midfielder Mads Bidstrup.
The club reportedly paid FC Copenhagen €2million for the junior international in the deal announced on Thursday.
Leipzig are also reportedly close to signing Portugal under-17 midfielder Umaro Embalo from Benfica, who like Bidstrup, will join RB’s academy.
These five youngsters are currently impressing in Germany’s top flight:
JADON SANCHO (Borussia Dortmund)
Sancho broke into the first team this month and has impressed on his two Bundesliga starts.
The 17-year-old winger hit the post against Wolfsburg a fortnight ago, causing havoc on the left wing, and set up Shinji Kagawa’s equaliser in last Friday’s 1-1 draw at Hertha Berlin.
LEON BAILEY (Bayer Leverkusen)
The Jamaica winger, 20, back-heeled an audacious seventh league goal and set up another when Leverkusen crushed Hoffenheim 4-1 last weekend.
He also has six assists this season to help Bayer climb to second and is currently believed to be worth double the €13.5million Leverkusen paid Belgian club Genk for him in January 2017.
JANN-FIETE ARP (Hamburg)
After scoring two hat-tricks for Germany at last year’s European Under-17 Championships, Arp made his Hamburg debut aged 17 in September, becoming the first Bundesliga player born this millennium.
The Hamburg academy product scored two goals in two games last October to become the club’s youngest scorer in the Bundesliga.
Having only turned 18 this month, Arp wants to help relegation-threatened Hamburg stay up while studying for his ‘Abitur’ – Germany’s university-entry exams.
CHRISTIAN PULISIC (Borussia Dortmund)
Still only 19, but already a US international and first-team regular having broken through from Dortmund’s academy in January 2017.
The attacking midfielder, born in Hershey, Pennsylvania, has hit three goals in 17 league games this season.
He scored and provided an assist in a 3-0 win over Wolfsburg on the opening day.
Just like his team, Pulisic‘s form dipped in Germany’s autumn as Dortmund dropped down the table having led by five points in September.
MICHAEL CUISANCE (Borussia Moenchengladbach)
‘Gladbach paid just 250,000 euros for the France under-19 talent from Nancy’s academy, but Cuisance, 18, has already made 12 appearances in Germany’s top flight.
He has started four Bundesliga matches and plays either in central or defensive midfield and showed his promise when he set up a goal in last September’s 2-0 win over Hanover.
Ghana international Kevin-Prince Boateng has defended Pierre-Emerick Aubameyang as the on-going saga of the Borussia Dortmund star’s possible move to Arsenal drags on after his falling out with the Bundesliga club.
Boateng has a history of falling out with management and said that the level of criticism Aubameyang was receiving was “wrong”.
“I know him very well, he’s a good friend of mine,” Eintracht Frankfurt midfielder Boateng told broadcaster Eurosport.
“The most important thing would be to just sit down (with Dortmund) and use clear words – that’s how you bring about some peace.
“But we must not forget what a great player he is and how much he has given to Dortmund.
“It’s wrong, too, that everyone’s piling in on top of him now.”
Aubameyang has scored 141 goals in 212 games for Dortmund in all competitions since his arrival in 2013.
He fell out with Dortmund after being suspended for the second time this season earlier in the month for turning up late to training.
Aubameyang was dropped for Dortmund’s last two league games and senior Arsenal figures were in the city last Sunday to negotiate a deal.
According to German media reports, Dortmund have rejected Arsenal’s improved bid of €58million for the 28-year-old.
Dortmund, sixth in Germany’s top flight, reportedly want €70million for the Gabon star, who has a Borussia deal until 2021.
OFFICIAL: Arsene Wenger confirms that a deal for Pierre-Emerick Aubameyang involving Olivier Giroud going the other way was never a possibility. pic.twitter.com/AvRk1gQs05
— Squawka News (@SquawkaNews) January 26, 2018
Gunners boss Arsene Wenger insisted Friday there is no development in the saga.
Dortmund head coach Peter Stoeger has even said Aubameyang could return to the team for Saturday’s league match against Freiburg.
Should a transfer fall through, Aubameyang will have to eat considerable humble pie.
He did little to endear himself to the German public after being photographed wearing a Dortmund shirt bearing the name “Dembele”.
Ousmane Dembele boycotted Dortmund training last August to force the club to sell him to Barcelona, where he eventually went for €105million.
Boateng, who left Schalke under a cloud in December 2015 after being indefinitely suspended the previous May, feels football clubs in general must show players who are boss.
“If someone returns too late from their holidays, then a fine is not the only thing that helps,” said Boateng. “You also have to sanction a player differently.”
“I think the clubs may have to do more to make it clear that they are the boss.”
Boateng knows all about getting on the wrong side of management.
He last played for Ghana at the 2014 World Cup, but left the tournament under a dark cloud after a row with then-coach James Kwesi Appiah.
But Boateng says being suspended by Schalke taught him a few lessons.
“The suspension at Schalke hurt me the most,” said Boateng, who has played in the England, Spain, Germany and Italy. “I was shown what it’s like when someone can obstruct your future.
“That’s where I got to know the football business: it does not matter who you are, what your name is, what you have achieved.
“If it does not work, you will be exchanged.”