A friend and a cousin of the complainant, who were at the club with her that night, told the court Alves invited them over to the VIP area where he was with a friend.
In emotional testimonies, they said Alves groped them and flirted with the complainant before they described the aftermath of the alleged assault. The court did not disclose their names.
"(Alves) had a creepy attitude. I felt tense," said the friend.
The former Barcelona defender was arrested in January last year and has since been held on remand in a jail outside the city.
The public prosecutor accuses Alves of forcing the woman to have sex and of not using a condom and is seeking a nine-year prison term and for Alves to pay damages worth 150,000 euros ($163,215) to his alleged victim.
Alves initially denied any sexual encounter with the woman whom he said he did not know. He later said he had consensual sex with her in the VIP bathroom of a nightclub, adding that he had denied it originally to protect his marriage.
After around 15 minutes, Alves left the restroom and a couple of minutes later the complainant followed, looking "devastated", the cousin said.
"She said she needed to go. We left to get our coats from the concierge and before getting there my cousin told me (Alves) had hurt her a lot and had ejaculated inside of her," the witness said.
Alves, dressed in blue jeans and a white shirt, sat on the front row in a courtroom at the Provincial Court of Barcelona, the highest in the province, as his trial began on Monday.
His mother, accompanied by one of his brothers, blew kisses and made a heart-shaped sign with her hands as Alves, handcuffed and escorted by police officers, entered the room.
The three-judge panel denied a request by Alves' lawyer Ines Guardiola for the trial to be suspended on the basis that he was not given enough time to prepare for his first police interview after his arrest and had suffered a parallel trial by media.
The case has attracted significant attention not only due to Alves' profile as one of the greatest players of all time.
Sexual assault is a dominant political theme in Spain, even more so after the alleged non-consensual kiss that then Spanish Football Federation chief Luis Rubiales planted on the lips of Jenni Hermoso after the team's World Cup triumph last August.
Alves' trial is one of Spain's highest profile since a 2022 law from the socialist-led government made consent a key factor in sexual assault cases and increased minimum jail time for such assaults involving violence.
The law was prompted by the 2016 gang-rape of a teenager during the San Fermin bull-running festival after the five men were originally convicted by a lower court of sexual abuse, sparking mass protests. The country's top court subsequently ruled they were guilty of rape.
The case triggered national soul-searching on the topic that continues to this day as gender violence rates remain high.
In Spain, a claim of rape is now investigated under the general accusation of sexual assault, with rape as an aggravating factor.
The Alves trial is expected to last three days.
The alleged victim testified on Monday in a closed doors session. She talked from behind a screen, with her voice distorted to protect her identity.
A total of 30 people will give evidence, with Alves due to take the stand last.
Alves has won more than 40 trophies for Brazil and clubs including Barcelona, Sevilla, Juventus and Paris St Germain. Following his arrest, he was fired by Mexico's Pumas UNAM.
