NEWBURYPORT – A Lynn man was convicted by a Superior Court jury Thursday afternoon of raping and beating his girlfriend at knifepoint in their Newhall Street home in 2009.Luis Mercado, 33, formerly of 45 Newhall St., #1, went on trial earlier this week in Newburyport Superior Court on charges of rape, two counts of assault and battery with a dangerous weapon, assault with a dangerous weapon and three counts of violation of a court order.A 12-person jury deliberated for just three hours before reaching their decision, finding Mercado guilty on all seven charges.Judge Richard E. Welch III delayed sentencing until this morning. In the meantime, Mercado remains held in the custody of the Essex County sheriff at the Middleton Jail and his bail was revoked.Assistant District Attorney James P. Gubitose successfully presented evidence at the trial that on or about Nov. 26, 2009 Mercado forced his then 24-year-old girlfriend to have sex with him at knifepoint at the Newhall Street apartment. The couple had been together for about three years and they have a child together.He faces up to 20 years in state prison on the rape charge and up to 10 years in prison on the assault and battery with a dangerous weapon.