The Sailors were able to take the lead in the 60th minute when Will Trujillo converted a penalty kick into the lower left corner of the goal.
Trujillo was struggling for a lose ball near the end line, right of the goal box, when he was taken down by an overzealous Costa Mesa defender.
"After I fell, I was pretty sure the penalty was going to be called," Trujillo said.
Trujillo scored his second goal of the match in the 68th minute. Midfielder Jeremy Anish made a low, arching cross from the right side of the goal. Trujillo trapped the ball in the area and was able to fire a shot past Costa Mesa goalkeeper Luis Munoz.
In the second half, Newport Harbor outshot Costa Mesa, 8-2. As the Sailors took the lead, they began to control the pace of the game, keeping the ball on the Mustangs' side of the field.
Costa Mesa got out to an early 1-0 lead on a score from Edson Diaz.
The senior midfielder converted a defelection with an over-the-head bicycle kick. The shot was undefendable, as the ball deflected of the bottom of the crossbar and into the goal.
Costa Mesa Coach Eugene Day said he felt optimistic despite the loss. "We came out to a quick start and that is something I stress for them to do," Day said. "I also like the way we moved the ball. We are finally keeping the ball on the ground instead of always relying on the long overhead passes."
Day pointed to his team's youth as one obstacle to overcome.
"These guys haven't played together that much," he said. We are starting two freshmen and five sophomores."
The victory came at a cost for the Tars. Trafford Hill suffered a sprained ankle after coming down awkwardly from a leaping shot midway through the second half.
Trujillo said he is confident his team will fare well in the Pacific Coast League, which opens next week.
"This team plays its hardest until the end of the game," Trujillo said. "That is something that is going to make us succeed in league play."
Both teams face rivalry games later in the week.
Costa Mesa will open Golden West League play against Estancia at 3:15 p.m. Wednesday at Orange Coast College.
Newport Harbor visits Corona del Mar at 3 p.m. Friday.
Newport Harbor 3,
Costa Mesa 1
Score by Halves