Tobin Heath has her eye on the ball as she scored Thursday night. (Rob Kinnan-USA TODAY Sports)

CARY, North Carolina — If they were any doubts as to the quality and focus of the U.S. national team, they were put to rest and then some at Sahlen’s Stadium in WakeMed Soccer Park Thursday night.

The relentless U.S. broke open a close game by scoring five goals in the second half to trounce Mexico in the Group A opener for both teams in the 2018 concacaf Women’s Championship.

Megan Rapinoe and Alex Morgan tallied two goals apiece and Tobin Heath and Julie Ertz each added one for the defending Women’s World Cup champions and the No. 1 team in the FIFA rankings.

The Americans took the group lead over Panama, 3-0 winners over Trinidad & Tobago in the opening game of the doubleheader, thanks to goal differential.

Deploying a high pressure, fast-paced attack, the U.S. dominated from the opening kickoff to the final whistle.

With the game barely three minutes into game, Rapinoe lifted the U.S. into a 1-0 lead as she knocked home a Lindsey Horan feed from the left side as goalkeeper Bianca Henninger ventured off her line to the right while going after the ball.

The Americans wore down the Mexicans in the final half.

After a long free kick crashed off the crossbar, Ertz drilled home the rebound into the lower left corner for a 2-0 lead in the 47th minute. Morgan headed in Rapinoe’s corner kick from five yards for a three-goal advantage in the 57th minute.

The U.S. was far from finished.

Heath recorded her 22nd international goal in the 61st minute. Overlapping left back Crystal Dunn, a Rockville Centre, N.Y. native and former member of the Albertson Fury, dribbled around two defenders and sent a cross to Heath. The forward headed it in from 10 yards for a 4-0 lead. Rapinoe’s second goal was a tap-in after second-half substitute Carli Lloyd won a ball in the penalty area in the 70th minute.

Morgan scored for her second and 92nd international goal in the 80th minute, slotting home Becky Sauerbrunn’s left-wing feed.

Goalkeeper Alyssa Naeher, who recorded the shutout, was never severely tested.

In the opening match, Panama, playing in its third CWC and first since 2006, secured its second win in the competition as the Central Americans bested T&T, which finished fourth in the 2014 CWC.

Panama’s 17-year-old goalkeeper Yenith Bailey recorded the clean sheet.

Marta Cox, who did not score during qualifying, lifted the Panama into a 1-0 lead in the 12th minute. A rather dubious Trinidad back pass deflected off Cox to captain Natalia Mills on the right side of the penalty area. Mills then slipped a pass to Cox, who finished from eight yards past goalkeeper Kimika Forbes.

An unmarked Kenia Rangel, who had a hat-trick in a qualifying win over El Salvador, doubled the lead in the 68th minute, scoring from seven yards for a 2-0 lead.

Minutes after entering the match, Erika Hernandez found herself unmarked in the area to score the final goal from six yards in the 88th minute.

On Sunday, the Americans meet Panama while Mexico takes on Trinidad.

The competition continues Friday night in Edinburg, Texas as Costa Rica meets Cuba and Canada plays Jamaica in a Group B opening doubleheader.