Kyle Busch's Son Takes Checkered Flag ... First Win After Dad's Death

Kyle Busch's 11-year-old son is doing his dad's legacy justice ... because he just won his first race since the NASCAR legend passed away.

Brexton Busch -- the eldest of Kyle and Samantha Busch's two kids -- competed in several events at Oklahoma’s Port City Raceway dirt track Friday ... and won the restricted micro sprint class division, according to the trade publication Motorsport.

Samantha posted about Brexton's victory on Instagram Saturday afternoon ... sharing scenes from the track.

Brexton -- outfitted in a bright green racing suit -- posed with his team in front of his car ... waving a checkered flag to signify his first place finish.

Samantha noted she felt so proud of -- and heartbroken for -- her son ... adding his determination and resilience in the face of adversity amaze her.

She ended her caption by writing, "Congratulations, buddy. Dad would’ve been so, so proud. ❤️🏁."

As you know ... Kyle passed away suddenly in May after a severe illness landed him in the hospital. 911 audio obtained by TMZ Sports indicated he was struggling to breathe, overheating and coughing up blood before medics rushed to help.

Authorities ultimately determined Busch died from severe pneumonia that progressed into sepsis.

The racing world mourned in the aftermath of his passing ... with numerous tributes in his honor taking place at racing events throughout the month of May.

Just a couple weeks ago, Samantha revealed she saw two rainbows she's convinced were signs sent by her husband ... so, it's certainly possible Brexton has a guardian angel on the track with him.

Busch was 41 years old.

RIP