Mace raised concerns about possible conflicts of interest after HS2 appointed CH2M European managing director Mark Thurston as its new chief executive last month.
HS2’s decision to award the deal to second placed Bechtel will allow it to avoid re-running the entire procurement process.
But Mace could still mount a challenge over the initial awarding of the contract, which holds out the possibility of a re-run.
The section of track covers construction of the Crewe to Manchester and West Midlands to Leeds lines.
An HS2 spokesman said: “HS2 Ltd can confirm that Bechtel are being taken forward to the next stage of the 2b Development Partner procurement process.
“The bidder now enters the standstill period allowed for under the process prior to contract award.
“Following discussions, we are confident they are able and prepared to deliver the contract on time, on budget and to a high standard.”
Transport Secretary Chris Grayling and HS2 chairman Sir David Higgins will be questioned about the issue by the Commons’ Transport Select Committee on Wednesday.