#1 Jeff Hardy (vs. Matt Hardy at WWE Backlash 2009)

The Hardy Boyz have had quite the run over the past couple of decades. Their tag team reached legendary status and are guaranteed to enter the WWE Hall of Fame unless Matt Hardy remains in AEW for a long time. Both him and Jeff Hardy have enjoyed success as singles stars as well.
They have faced each other many times over the years, most notably in the Final Deletion in IMPACT Wrestling. Matt and Jeff did have a bitter rivalry in WWE as well, resulting in a couple of brutal matches on pay-per-view.
After costing Jeff Hardy the WWE Championship and admitting to being behind several horrible occurrences in his life, Matt Hardy defeated his brother at WrestleMania 25. The two had an Extreme Rules Match which ended with Matt hitting a Twist of Fate with a chair around Jeff's head.
However, this list is about current WWE stars defeating their relatives. That happened at the very next pay-per-view, Backlash. Jeff Hardy won a similarly brutal 'I Quit' Match, by tying his brother to a table and threatening to jump onto him from a tall ladder.
Despite winning the match after Matt quit, Jeff hit his brother with a leg drop through the table. This was representative of the careers of the Hardys as singles stars in WWE. Jeff Hardy would go on to win the World Heavyweight Championship shortly after this victory, while Matt Hardy toiled around in the midcard.