# 2021 Knoxville Challenger – Singles

Michael Mmoh was the defending champion but lost in the semifinals to Daniel Altmaier.
Christopher Eubanks won the title after defeating Altmaier 6–3, 6–4 in the final.

## Seeds

* Tennys Sandgren (first round)
* Daniel Altmaier (final)
* Vasek Pospisil (first round)
* Mitchell Krueger (second round)
* Jack Sock (quarterfinals)
* J. J. Wolf (first round)
* Dmitry Popko (first round)
* Bjorn Fratangelo (semifinals)

## 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 |
| 8 | Bjorn Fratangelo | 5 | 5 | | | | | |
| | Christopher Eubanks | 7 | 7 | | | | | |
| | Christopher Eubanks | 7 | 7 | | | Christopher Eubanks | 6 | 6 |
| | | | | | 2 | Daniel Altmaier | 3 | 4 |
| | Michael Mmoh | 6 | 3 | 4 | 2 | Daniel Altmaier | 3 | 4 |
| 2 | Daniel Altmaier | 3 | 6 | 6 | | | | |

### 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 | Semifinals | Semifinals | Semifinals | Semifinals |
| 1 | T Sandgren | 6 | 6$^3$ | 6$^4$ | | | | | | | | | | | | | |
| Alt | P Polansky | 3 | 7$^7$ | 7$^7$ | Alt | P Polansky | 6 | 6$^2$ | 0$^r$ | | | | | | | | |
| WC | Em Nava | 6 | 6 | | WC | Em Nava | 2 | 7$^7$ | 0 | | | | | | | | |
| Q | D Young | 3 | 2 | | | | | | | WC | Em Nava | 4 | 4 | | | | |
| Q | G Brouwer | 5 | 6 | 7 | | | | | | 8 | B Fratangelo | 6 | 6 | | | | |
| Q | JC Aragone | 7 | 2 | 5 | Q | G Brouwer | 3 | 6 | 3 | | | | | | | | |
| | Yo Watanuki | 4 | 6$^5$ | | 8 | B Fratangelo | 6 | 3 | 6 | | | | | | | | |
| 8 | B Fratangelo | 6 | 7$^7$ | | | | | | | | | | | 8 | B Fratangelo | 5 | 5 |
| 3 | V Pospisil | 6 | 2 | 3 | | | | | | | | | | | C Eubanks | 7 | 7 |
| | C Eubanks | 2 | 6 | 6 | | C Eubanks | 6 | 2 | 7$^7$ | | | | | | | | |
| | G Soeda | 6 | 7$^8$ | | | G Soeda | 3 | 6 | 6$^4$ | | | | | | | | |
| Alt | M Jaziri | 4 | 6$^6$ | | | | | | | | C Eubanks | 6 | 7$^{11}$ | | | | |
| | J Jung | 6 | 6 | | | | | | | Alt | C Harrison | 3 | 6$^9$ | | | | |
| | J Kubler | 4 | 1 | | | J Jung | 6 | 6$^3$ | 2$^r$ | | | | | | | | |
| Alt | C Harrison | 6 | 6 | | Alt | C Harrison | 3 | 7$^7$ | 4 | | | | | | | | |
| 6 | J. J. Wolf | 2 | 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 |
| 7 | D Popko | 4 | 5 | | | | | | | | | | | | | | | | |
| Q | A McHugh | 6 | 7 | | Q | A McHugh | 6 | 6 | | | | | | | | | | | |
| | A Vukic | 3 | 6 | 5 | | S Kozlov | 4 | 4 | | | | | | | | | | | |
| | S Kozlov | 6 | 4 | 7 | | | | | | Q | A McHugh | 6 | 3 | 1 | | | | | |
| | Y Uchiyama | 5 | 3 | | | | | | | | M Mmoh | 3 | 6 | 6 | | | | | |
| | M Mmoh | 7 | 6 | | | M Mmoh | 7$^7$ | 1 | 6 | | | | | | | | | | |
| PR | T Ito | 6$^4$ | 3 | | 4 | M Krueger | 6$^4$ | 6 | 2 | | | | | | | | | | |
| 4 | M Krueger | 7$^7$ | 6 | | | | | | | | | | | | | M Mmoh | 6 | 3 | 4 |
| 5 | J Sock | 7$^7$ | 7 | | | | | | | | | | | | 2 | D Altmaier | 3 | 6 | 6 |
| WC | A Kovacevic | 6$^4$ | 5 | | 5 | J Sock | 6 | 7$^7$ | | | | | | | | | | | |
| | P Gunneswaran | 6 | 7$^7$ | | | P Gunneswaran | 3 | 6$^1$ | | | | | | | | | | | |
| | M Torpegaard | 2 | 6$^2$ | | | | | | | 5 | J Sock | 6 | 5 | 6$^2$ | | | | | |
| | B Rola | 6 | 7$^7$ | | | | | | | 2 | D Altmaier | 3 | 7 | 7$^7$ | | | | | |
| | T-S Kwiatkowski | 3 | 6$^5$ | | | B Rola | 6$^3$ | 4 | | | | | | | | | | | |
| WC | A Walton | 3 | 2 | | 2 | D Altmaier | 7$^7$ | 6 | | | | | | | | | | | |
| 2 | D Altmaier | 6 | 6 | | | | | | | | | | | | | | | | |