“The South African defence were punishing us for that so we just need to be stronger in terms of the setups and the balls that we’re trying to take.”
Williams did, however, feel England showed “tenacity” after half-time, adding: “I’m so proud of my girls in the way that they kept fighting.
“We need a big response now to come back and win the double header at the weekend.”
Both England and South Africa are building towards this summer’s Commonwealth Games in Glasgow, where the two sides are in the same six-team pool.
Jess Thirlby’s England are fourth in the world rankings, with South Africa close behind in fifth.
They next face each other on Saturday at 15:00 GMT, before playing the final game in the series on Sunday at 14:00.