Kenley Jansen’s downfall in the ninth inning of the Dodgers ’ 8-5 loss at Petco Park on Sunday began in ordinary fashion, with a leadoff single through the left side.

Instead of attempting a barehanded play and tough throw across his body, Justin Turner let the ball roll, hoping it’d go foul.

Not after storming from behind to snag victories Friday and Saturday from an upstart club striving to prove they belong in the Dodgers’ stratosphere.

No, it was just a matter of when — a feeling coursing through Petco Park that magnified once Max Muncy whacked a three-run blast in the sixth inning.

Franmil Reyes emphatically opened the scoring for the Padres in the first inning, banging a fastball 458 feet nearly to the video board overlooking left field.

San Diego doubled the margin in the fourth inning, which started with Maeda issuing a leadoff walk to Eric Hosmer.