Captain Jake Wright has admitted Oxford were far from at their best in the second half of their 1-0 weekend defeat to Crewe.
The Us played good football for the opening period against Alex but ultimately had to settle for nothing, as debutant Greg Pearson netted a late winner for the visitors.
And Wright conceded their display after half-time at the Kassam Stadium was not good enough.
He told the club's official website: "I think in the first half-hour we looked good going forward and solid at the back. The lads up front were knocking it about well and creating a few half-chances but then we came out in the second half and were really poor.
"We weren't creating chances, we weren't passing as well and the options were difficult.
"In the first half we had three or four options but in the second they weren't really there. It was frustrating and a disappointing result."