1
general::
So close that the advantage or lead shifts from one to the other or is virtually indistinguishable, as in The two are neck and neck in developing a new operating system for the computer. The term comes from horse racing, where the necks of two horses in competition appear to be side by side. [Early 1800s] For a synonym, see NIP AND TUCK.
American Heritage Idioms
2
general::
Phrase(s): neck and neck
Fig. exactly even, especially in a race or a contest. • John and Tom finished the race neck and neck. • Mary and Ann were neck and neck in the spelling contest. Their scores were tied.
McGrawhill's American Idioms And Phrasal Verbs