"It's important not to overanalyze these games," said midfielder Michael Bradley, who set up the first goal with a gorgeous chip.
"There's a World Cup coming up and everybody wants to now look at every play in every minute in every game, but it's important to now look at these games in the context of a bigger picture."
Tim Howard made his 99th international appearance, and with his 54th win surpassed Kasey Keller to set the U.S. record for wins by a goalkeeper. Other than that, the way the U.S. played was far more significant than the result.
"Quite an open game," coach Jurgen Klinsmann said. "We still want to see a lot of little pieces."
Klinsmann made the decision 10 days earlier to cut American career scoring leader Landon Donovan, who got his third goal in two games for the Los Angeles Galaxy on Sunday.
Klinsmann's roster, lineup picks and formation choices are highly debated by a growing American fan base.
The 26-year-old Johnson, among the five German-Americans on the 23-man roster, made his second straight start at right back. He received a backpass about 40 yards from goal in the 26th minute, made a run and laid the ball off to Bradley. Johnson continued his run, Bradley chipped the ball over the defense and Johnson coolly slotted past goalkeeper Onur Kivrak with a left-footed volley from 6 yards.
"He kind of told me with the way he was running that he was going to keep running through," Bradley said
Johnson, who had not scored in 20 previous national team games, jogged down the endline with both arms outstretched, stopped, turned and gave Dempsey a double high-5.
"On his celebration, you could see that he's not an experienced goal-scorer," Klinsmann said.
Johnson joked about his lack of preparation for jubilation.
"I'm a defender. On this part a Jozy or a Clint are better," he said.
Jozy Altidore, who started alongside Dempsey in the 4-4-2 formation with a diamond midfield, remained scoreless in six international matches since October.
Altidore put the ball into the goal in the 15th minute after Kivrak saved Matt Besler's header off a corner kick, but Tunisian referee Slim Jedidi called a foul on Altidore for pushing the goalkeeper. Altidore was saved on a breakaway in the 71st, but Jedidi had whistled off the play for a foul on defender Hakan Balta. Altidore broke in with a nice move in the 81st only for Kivrak to block his shot.
Dempsey, who missed Tuesday's win over Azerbaijan because of a sore groin, made it 2-0 in the 52nd with his 37th international goal, joining Eric Wynalda and Brian McBride as the only Americans to score in 10 consecutive years.
U.S. vs. Nigeria
O International exhibition
Thursday, 4 p.m.
TV • ESPN