Second-half goals from Ajax striker Klaas Jan Huntelaar and man-of-the-match Robin van Persie secured a 2-0 win and ensured the Oranje topped group C with maximum points.
Their reward was a quarterfinal meeting with either Sweden or Russia in Basel on Saturday, and van Basten was justifiably proud of the professional job his second-string side he sent out had done, albeit against opponents who displayed an almost inexplicable lack of ambition.
"We have to be very proud and happy that we have won the group and the three games," said van Basten. "We have made a great start. But Saturday is another match altogether and we have to start again from zero.
"We will be in front of our television screens watching the Sweden v Russia match and we will try to do a good analysis of whoever it is we have to play."
The defeat of the Romanians ensured van Basten's squad did a huge favour to Italy coach Roberto Donadoni, his old friend and AC Milan team-mate.
Italy joined the Dutch in the quarterfinals after beating France 2-0 and van Basten denied reports that Donadoni had been in touch with him before the final round of group matches.
"I know him very well but I also know in a situation like that it is not good to have contact with each other," van Basten said. "In the end, I'm happy for him, happy for Italy."
Van Basten made no apology for fielding a weakened side for the final group match. "I had a very simple reasoning," he said. "We were already qualified, and had two difficult matches, physically and mentally.
"Hopefully we will be able to play more matches in the tournament and it is going to require a lot of mental and physical exertion so it was an ideal opportunity to put other players into the team."
Van Basten now believes his side can go on emulate the squad he inspired to victory in the 1998 European Championships.
"The atmosphere is good. The players are working well together and having a good time. If we continue playing like this I don't know where exactly we are going to end but I hope it is going to take a long time," van Basten said.
Although needing to win to be sure of staying in the competition, Romania's only concern appeared to be to avoid the kind of mauling the Dutch had handed out to France and Italy in their first two group matches.
That was never on the cards with only rightback Khalid Boulahrouz and the defensive midfielder Orlando Engelaar surviving from the Dutch side that had started the 4-1 demolition of France.
But van Basten's side were always in control and would have ended the contest much earlier if Huntelaar and Arjen Robben, who was withdrawn after an hour, had taken their first-half chances.
Romania coach Victor Piturca admitted the Dutch had been "better and fresher" than his side, who he felt had paid a high price for their efforts in securing draws with France and Italy.
"Not losing the first two matches against the world champions and the vice champions has been an achievement for our team. But we could not change the players who played in those matches and they took a lot out of us. Maybe we were a bit tired."
After Huntelaar and Robben had wasted good chances before the break, Holland's breakthrough finally came when Ibrahim Afellay's cross from the right was flicked on by Orlando Engelaar.
Huntelaar demonstrated his predatory instincts remain intact by prodding in his eighth goal in 13 international appearances.
Romania's only real chance of the entire match came a minute from the break.
Razvan Rat made it to the byline and cut the ball back for Paul Codrea, who blasted his free shot over from just inside the box.
The Romanians also had a brief flurry of pressure in the closing minutes but it was to be van Persie who had the final word, holding off Cosmin Contra's challenge before firing home.
AFP
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