Just as in last weekend's Premier League opener against Crystal Palace, Soldado was on target from the penalty spot against Swansea.
The Spain striker, who also scored twice in the Europa League on Thursday, slotted past Michel Vorm in the 58th minute after Andros Townsend was fouled by Jonjo Shelvey.
Soldado's goals are softening the blow of losing Gareth Bale, who is on the verge of joining Real Madrid and hasn't played as the transfer has been negotiated.
Swansea, though, have opened the season with consecutive losses.