The 20-year-old centre was one of 12 players ordered back to England as a cost-cutting measure. But the tour coach, Phil Larder, argued successfully that he needed extra cover in the backs and Senior, who appeared as a substitute in the first Test defeat in Auckland last week, was the man he wanted.
"I felt we needed some back-up in the backs, but Keith is the only player we will be keeping on," Larder said. "I feel that we are adequately covered elsewhere now."
Senior said that he only found out about his reprieve when he returned to his hotel room in Auckland after a late night out that was intended to be his farewell to New Zealand.
Larder also has Tony Smith, Adrian Morley and Bernard Dwyer as cover for the 17 selected for today's second Test. Smith, who has been in hospital with an infected arm, is expected to be fit in time for the final Test, in Christchurch next Friday.