The 22-year-old utility man, who has not made a senior appearance for the club since April last year, got 84 minutes under his belt in the reserves' 2-1 defeat by Hartlepool on Wednesday.
Australia international Williams had previously played part of two training ground games as he attempts to build himself back up after a lengthy lay-off with a pelvic condition.
The injury prevented him from representing his country at last summer's World Cup finals in South Africa and has robbed his club of the services of a man who has lined up in midfield and defence during his time on Teesside.
Williams would be a welcome addition to Mowbray's squad as the manager prepares for a vital final 13 npower Championship games with his side lying just two places and six points above the relegation zone.
Source: PA
Source: PA