How to capture 2 fields, the first part of this word (LON) and the remaining (RTI2_SND.TRACE) within the same regex?

[Bradd23]

Hi i'm trying to capture 2 fields, the first part of this word (LON) and the remaining (RTI2_SND.TRACE) within the same regular expression

LON_RTI2_SND.TRACE

Thanks

[ITWhisperer]

(?<first>[^_]*)_(?<rest>.*)