Chicago- After several delays, including a brief one this morning, the prosecution’s key witness gave explosive testimony Monday.

The prosecution’s key witness in the trial of singer R. Kelly on child pornography charges told jurors about three sexual encounters she had with Kelly and the alleged victim in the case.

In just under one hour of testimony, Lisa Van Allen, 27, also identified Kelly and the alleged victim on the videotape that is the central piece of evidence in the trial.

Van Allen, who was 17 when she first met Kelly, testified to a sexual encounter with the underage girl in 1998, 1999 and in 2000. Two of those encounters were videotaped, she said, though neither tape is the one at the center of the prosecution’s case.

Van Allen, now engaged and the mother of a 5-year-old-girl, first met Kelly at the video shoot for “Home Alone” in late 1997 or early 1998, where after a brief introduction the two engaged in sexual intercourse, she testified in court today.

After exchanging phone numbers, Van Allen, of Georgia, started flying to Chicago to visit the recording artist, dividing her time between a hotel room paid for by Kelly and the studio where he recorded his music. By the summer of 1998, the 17-year-old quit her job in Georgia and moved to Chicago to be with Kelly, she testified.

She attended his performances and went on tour with him, in addition to occasional outings to the mall for shopping, she said.

Then in late 1998, Van Allen testified she met the alleged victim. Their first encounter was sexual, she said, and took place with Kelly in the log-cabin themed room of his former home in Chicago.

The singer videotaped the encounter, she said.

“He had a stand, and he set it up … and directed it toward where we were,” she said under direct examination from the prosecution. “[He] told us where to sit and basically what to do.”

After the first encounter, she occasionally saw the alleged victim at Kelly’s music studio, Van Allen said. Then a year later, she said, they all met up again at the singer’s house, where the three engaged in intercourse on a black futon set up on the singer’s basketball court.

Van Allen said Kelly again set up a video camera and pointed it at the mattress. But this time, Van Allen started crying, she testified.

“I didn’t want to do it,” she explained in court. “[Kelly] stopped everything and put up the camera and we left.”

The last encounter between the three took place in 2000 in Kelly’s trailer at the video shoot for “A Woman’s Threat” in Chicago, she testified.

She said Kelly recorded the encounter, as well, though it was interrupted when someone came knocking on the trailer door.

“[The alleged victim] had to run into the bathroom naked” because Kelly did not want her to be seen, Van Allen said.

The prosecution made clear that neither this tape nor the other recordings she testified about were the tape shown to jurors during the trial.

Van Allen said she had never seen that tape before prosecutors showed it to her last week. But her identification of the participants in the video was unequivocal: the alleged victim and Kelly.

She said the tape was probably made in 1998, the same year she was first filmed with the alleged victim and Kelly, because “they both looked exactly the same way.”

Van Allen added that she recognized the room where the encounter between the alleged victim and Kelly took place as the log cabin-themed room. Van Allen testified that Kelly kept all of his tapes with him at all times and put them in a black duffel bag.

“If he was in the studio, it was in the studio with him. If he went to Hoops [basketball court], it went to Hoops with him,” she said. “The bag would follow him.”

Van Allen testified that in 2001, she left Kelly and returned to Georgia. She maintained contact with the singer, though, and he visited her in Atlanta.

During one visit, she testified, she stole his Rolex watch.

Defense attorneys had previously mentioned the theft, and they are likely to hammer away at her during cross-examination. The defense is expected to attack her credibility as a witness, citing her theft and other charges leveled against her.

As for her reasoning for coming forward: “It was the right thing to do.” She was also given state and federal immunity for testifying in the case, Van Allen said.

The defense is likely to question her motivation, given that she waited several years after the indictment was announced before coming forward.

Van Allen admitted on the witness stand that she had been in jail for a month after a fight with another woman when she was 19. She also acknowledged she spent two days in jail for a domestic battery charge in 2006 after finding her boyfriend with another woman.

Kelly’s attorneys are expected to accuse her of offering to switch her testimony for a price. The defense team has described it as an extortion attempt, and unsuccessfully petitioned Cook County Judge Vincent Gaughan to compel the prosecution to file criminal charges against her.