Ryan Smyth, captain Dustin Brown, Andrei Loktionov, Wayne Simmonds and Michal Handzus each had a goal and an assist for the Kings, who lit up their crosstown rivals' rebuilt defense and backup goalie Curtis McElhinney.
Kyle Clifford also scored and Jonathan Quick made 24 saves for the Kings, who scored four power-play goals.
Todd Marchant scored two goals for the Ducks, who got 34 saves from McElhinney. Sexton and Marchant scored 40 seconds apart late in the third period after Los Angeles had taken a seven-goal lead.
Los Angeles scored just six goals in its first three exhibitions combined, but the power-play unit led by star defensemen Drew Doughty and Johnson clicked from the start against Anaheim.
The Kings outshot the Ducks 23-7 and took a 4-0 lead in the first period, battering McElhinney from every angle. After Brown got Los Angeles' opening late in a two-man advantage, Simmonds added another power-play score 38 seconds later.
Doughty and Johnson were on the ice for both scores, picking right up where they left off as a brutally effective power-play duo in last season's playoffs against Vancouver.
Marchant scored early in the second, but Handzus tapped home a loose puck back later in the period for another power-play goal. The Kings then scored three straight goals in the third period, including Johnson's second score for the top power play unit.
Enforcers George Parros and Kevin Westgarth fought to a draw in the second period, with the two Princeton alumni tumbling to the ice together and getting up to continue the fight in one fluid motion. Westgarth is expected to make the Kings' roster after racking up 25 points and 180 penalty minutes in the AHL last season.
Kings prospect Brayden Schenn and Ducks defenseman Luca Sbisa also had an entertaining fight in the final minutes. The bout was a rematch of a memorable bout between the two in juniors last season.