# 2021 Rancho Santa Fe Open – Singles

You Xiaodi was the defending champion but chose not to participate.
Rebecca Peterson won the title, defeating Elvina Kalieva in the final, 6–4, 6–0.

## Seeds

* Rebecca Peterson (champion)
* Fiona Ferro (semifinals, retired)
* Madison Brengle (semifinals)
* Zarina Diyas (second round)
* Misaki Doi (first round)
* Kristína Kučová (quarterfinals)
* Renata Zarazúa (first round)
* Polona Hercog (quarterfinals)

## Draw
### Key

* Q = Qualifier
* WC = Wild card
* LL = Lucky loser
* Alt = Alternate
* SE = Special exempt
* PR = Protected ranking
* ITF = ITF entry
* JE = Junior exempt
* w/o = Walkover
* r = Retired
* d = Defaulted
* SR = Special ranking

### Finals

| Semifinals | Semifinals | Semifinals | Semifinals | Semifinals | Final | Final | Final | Final |
| 1 | Rebecca Peterson | 6 | 6 | | | | | |
| 3 | Madison Brengle | 4 | 2 | | | | | |
| 3 | Madison Brengle | 4 | 2 | | 1 | Rebecca Peterson | 6 | 6 |
| | | | | | Q | Elvina Kalieva | 4 | 0 |
| Q | Elvina Kalieva | 4 | 6 | 3 | Q | Elvina Kalieva | 4 | 0 |
| 2 | Fiona Ferro | 6 | 4 | 0$^r$ | | | | |

### Top half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 1 | R Peterson | 6 | 6 | | | | | | | | | | | | | | | |
| WC | H Chang | 1 | 0 | | 1 | R Peterson | 6 | 6 | | | | | | | | | | |
| | M Hibi | 6 | 6 | | | M Hibi | 1 | 1 | | | | | | | | | | |
| Q | M Partaud | 3 | 3 | | | | | | | 1 | R Peterson | 6 | 6 | | | | | |
| Q | A Krueger | 2 | 2 | | | | | | | | L Cabrera | 4 | 1 | | | | | |
| SE | E Bektas | 6 | 6 | | SE | E Bektas | 6 | 1 | 6$^5$ | | | | | | | | | |
| | L Cabrera | 6 | 6 | | | L Cabrera | 4 | 6 | 7$^7$ | | | | | | | | | |
| 7 | R Zarazúa | 2 | 2 | | | | | | | | | | | | 1 | R Peterson | 6 | 6 |
| 3 | M Brengle | 6 | 6 | | | | | | | | | | | | 3 | M Brengle | 4 | 2 |
| WC | A Kiick | 0 | 2 | | 3 | M Brengle | 6 | 6 | | | | | | | | | | |
| | R Marino | 6 | 6 | | | R Marino | 1 | 2 | | | | | | | | | | |
| | M Inglis | 4 | 3 | | | | | | | 3 | M Brengle | 4 | 6 | 6 | | | | |
| | K Kozlova | 7 | 6 | | | | | | | | K Kozlova | 6 | 1 | 4 | | | | |
| Q | T Mihalíková | 5 | 2 | | | K Kozlova | 2 | 6 | 6 | | | | | | | | | |
| WC | K Day | 3 | 6 | 6 | WC | K Day | 6 | 3 | 2 | | | | | | | | | |
| 5 | M Doi | 6 | 4 | 3 | | | | | | | | | | | | | | |

### Bottom half

| First round | First round | First round | First round | First round | Second round | Second round | Second round | Second round | Second round | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Quarterfinals | Semifinals | Semifinals | Semifinals | Semifinals | Semifinals |
| 8 | P Hercog | 6$^5$ | 6 | 7 | | | | | | | | | | | | | | | |
| WC | J Failla | 7$^7$ | 3 | 5 | 8 | P Hercog | 6 | 6 | | | | | | | | | | | |
| Q | E Douglas | 7$^7$ | 3 | 6 | Q | E Douglas | 4 | 2 | | | | | | | | | | | |
| Q | M Manasse | 6$^4$ | 6 | 2 | | | | | | 8 | P Hercog | 4 | 3 | | | | | | |
| Q | D Hewitt | 5 | 6 | 2 | | | | | | Q | E Kalieva | 6 | 6 | | | | | | |
| Q | E Kalieva | 7 | 1 | 6 | Q | E Kalieva | 6 | 2 | 6 | | | | | | | | | | |
| | L Küng | 0 | 1 | | 4 | Z Diyas | 4 | 6 | 2 | | | | | | | | | | |
| 4 | Z Diyas | 6 | 6 | | | | | | | | | | | | Q | E Kalieva | 4 | 6 | 3 |
| 6 | K Kučová | 4 | 6 | 6 | | | | | | | | | | | 2 | F Ferro | 6 | 4 | 0$^r$ |
| JE | E Jacquemot | 6 | 4 | 2 | 6 | K Kučová | 1 | 7$^7$ | 7$^7$ | | | | | | | | | | |
| Q | H Giavara | 5 | 0 | | PR | P Hon | 6 | 6$^4$ | 6$^4$ | | | | | | | | | | |
| PR | P Hon | 7 | 6 | | | | | | | 6 | K Kučová | 6$^6$ | 6 | 4 | | | | | |
| | K Kawa | 1 | 4 | | | | | | | 2 | F Ferro | 7$^8$ | 3 | 6 | | | | | |
| | Ar Rodionova | 6 | 6 | | | Ar Rodionova | 2 | 2 | | | | | | | | | | | |
| | C Dolehide | 2 | 7 | 2 | 2 | F Ferro | 6 | 6 | | | | | | | | | | | |
| 2 | F Ferro | 6 | 5 | 6 | | | | | | | | | | | | | | | |