The Oranje maintained their perfect record in World Cup qualifying as two goals from Robin van Persie helped them to a convincing win at the Amsterdam ArenA which keeps them seven points clear at the top of Group D after six games.
Rafael van der Vaart opened the scoring in the 11th minute, Van Persie struck twice after the break - the second a penalty - and Jeremain Lens added a fourth in the last minute.
Van Gaal, who replaced Bert van Marwijk after a disastrous Euro 2012 campaign, paid tribute to his side's all-round display.
He told reporters: "I thought it was the best match in this period under me.
"Only in the third quarter were we sloppy but Romania created just this one chance. "But beyond that quarter we have done what we had agreed. And there you have the result.
"I have said that we are (taking) more steps and we have to believe in ourselves."
Van Persie has scored just once in 10 games - and none at all in seven - for Manchester United but his drought has not extended to the international stage.
Instead, the 29-year-old has three goals in two matches following his strike against Estonia last Friday and he also provided the ball for Van Der Vaart's opener last night.
Van Gaal eulogised about his contribution, saying: "Van Persie was very unlucky in the first half but in the second half he was actually very happy.
"He scored an incredible world-class goal - it was a ball he could barely head but he deliberately hit it into the top corner.
"And the penalty he placed well inside (the goal)."
"He was also a great target man which you saw with his first goal. And Van der Vaart also put his shot in flawlessly.
"And everyone contributed. Lens was also involved in two goals. And I'm not even talking about the defensive organisation."
Despite his unconfined praise of his team, Van Gaal does not see his side as favourite to lift the World Cup next year.
He said: "We are on our way to the World Cup in Brazil. But for now we are not there yet.
"I think the objective of the KNVB would be to make the semi-finals."