Prior to the pair, Connie Smith had held the book among women with 12 straight career-opening Country Songs top 10 singles (1964-68).
Swift and Underwood's streaks are the best among all artists since Tracy Lawrence arrived with 19 consecutive top 10s in 1991-97.
The two female stars are likely decades, however, from breaking the chart's all-time out-of-the-gate top 10 mark among all artists.
