Paul Zambra (35) of Inagh Road, Ballyfermot, has pleaded not guilty to murdering the 36-year-old on Donaghmore Avenue, Tallaght on November 14, 2007.
Ms Bates told the opening day of the trial that her partner was awake in bed when she left home at 8.40am that day to drive her children to school. She went straight to work after the school run, she said.
She recalled that later that morning a friend came to her at her workplace.
Denis Vaughan Buckley, prosecuting, had already told the jury that this friend had gone to her workplace after failing to get an answer from the deceased when he knocked on the couple's door.
Ms Bates explained that she drove home, went inside, straight up the stairs and into the front bedroom.
"Sean was in bed. I called his name and he wouldn't answer," she sobbed.
"I walked over. I saw blood at the side of the pillow," she recalled.
"He was just white. I knew by the way he was lying, his jaw, his mouth was open," she continued. "I just started screaming."
A neighbour gave evidence of seeing two men in balaclavas getting into a Cork-registered car near the scene at about 9.40 that morning.
"They were covered up," testified Sheila Mooney, adding that both men were wearing thick gloves.
"It was like a ski suit and he had his hood pulled right down," she said of the passenger's clothing. "The driver was wearing the same kind of ski suit."
The jury also heard from Detective Garda Padraig Mullarkey, who was on patrol with a colleague.
He said that as they drove past Belfry Dale, they saw a beige Volvo burst into flames.
He said he contacted Command and Control for a 'reg check' and was informed that the car was stolen.
The trial has now entered legal argument before Mr Justice Patrick McCarthy and will resume before the jury tomorrow.