Southampton manager Nathan Jones said the "blame lies solely with me" as bottom-of-the-table Saints lost to Nottingham Forest for their sixth successive Premier League defeat.
Forest recorded their first away league win of the season and moved out of the relegation zone, with Taiwo Awoniyi scoring the only goal at St Mary's.
In the 27th minute, Lyanco carelessly lost possession on the halfway line with Brennan Johnson capitalising and racing clear before he pulled it back for Awoniyi, who buried the chance - only Forest's second away league goal of 2022-23.
The Saints failed to have a shot on target and are yet to pick up a single point from four matches since Jones replaced the sacked Ralph Hasenhuttl in November.