The Manchester United star netted twice to take his tally for Oranje to 34 goals in 74 appearances and maintain the side's perfect record
Rafael van der Vaart gifted the Dutch an early lead with a low shot form the edge of the area, before Robin van Persie made it two after the break with a good header after Arjen Robben's excellent cross.
The Manchester United striker doubled his personal tally half-way through the second half when he converted a spot kick, with Jeremain Lens making it four in the closing minutes of the game.
The home side started the match with attacking intentions, and came close to opening the scoring in the early stages on a number of occasions. Kevin Strootman first saw his shot saved by Costel Pantilimon, before Van Persie aimed too high from close range after a superb cross from Lens.
However, Netherlands did grab the lead after 12 minutes, after more good work from Lens. The PSV winger reached Van Persie on the edge of the box with a low cross from the right, who then laid the ball off for Van der Vaart. The Hamburg star did not hesitate and beat Pantilimon with a right-footed shot from 18 yards out.
Romania got back into the match after Oranje's early opener, and almost restored parity after 38 minutes of play. Right-winger Adrian Popa tried his luck with a low shot from a narrow angle, but Kenneth Vermeer pulled off a superb save to keep his side in the lead.
Holland got a good chance to double their lead shortly after the break following some sloppy defending from Florin Gardos. The Steaua Bucharest defender failed to clear a cross from Strootman, but Van Persie's shot lacked accuracy, allowing Pantilimon to make an easy save.
The hosts continued to dominate proceedings in the second half and Van der Vaart should have doubled their lead in the 53rd minute. Daley Blind beat Gabriel Tamas to the ball in the corner before firing in a low cross for the HSV midfielder, who scooped the ball over the bar from close range.
Oranje did get their second goal of the game shortly after, though. Robben reached Van Persie with a perfect cross after going past his marker down the left, and the forward beat the Romanian goalkeeper with a subtle header.
Cristian Tanase could have pegged one back for Romania after some sloppy play from Holland in midfield, but the attacking midfielder inexplicably fired wide from long range rather than take his time and charge forward before trying his luck.
Lens continued to cause the guests all kinds of trouble with his dribbles down the right, and the referee had no other choice but to award Netherlands a spot kick after Gardos fouled the PSV attacker. Van Persie stepped up and coolly slotted home to surpass Johan Cruyff's goal tally and make it 3-0 with his 34th international goal.
Things would get even worse for the away side in the closing stages of the game when Lens added his name to the score sheet. Pantilimon failed to hold on to Adam Maher's powerful shot and the PSV star tapped home from close range to pour even more salt in Romania's wounds.
Oranje sit atop of Group D with 18 points from six games, while Romania have to settle for third spot for now with 10 points.