| 28‑Sep‑2020 | Roland Garros | Clay | Q3 | 123 | 144 | (31)Nikola Milojevic [SRB] d. (13)Mayer | 6-7(4) 6-2 6-3 | | 0.75 | 2.6% | 1.7% | 62.4% | 63.0% | 52.3% | 6/10 | 2:38 |
| 28‑Sep‑2020 | Roland Garros | Clay | Q2 | 123 | 149 | (13)Mayer d. Carlos Taberner [ESP] | 6-3 6-3 | | 1.34 | 11.5% | 3.8% | 59.6% | 71.0% | 38.1% | 1/4 | 1:26 |
| 28‑Sep‑2020 | Roland Garros | Clay | Q1 | 123 | 205 | (13)Mayer d. Peter Polansky [CAN] | 7-5 6-0 | | 1.50 | 5.7% | 11.3% | 41.5% | 77.3% | 58.1% | 2/3 | 1:26 |
| 14‑Sep‑2020 | Rome Masters | Clay | Q2 | 123 | 249 | (WC)Lorenzo Musetti [ITA] d. Mayer | 7-6(4) 6-3 | | 0.88 | 5.2% | 5.2% | 44.8% | 80.8% | 53.1% | 0/2 | 1:42 |
| 14‑Sep‑2020 | Rome Masters | Clay | Q1 | 123 | 470 | Mayer d. (Alt)Jacopo Berrettini [ITA] | 6-3 6-2 | | 1.48 | 9.6% | 9.6% | 53.8% | 78.6% | 50.0% | 3/5 | 1:11 |
| 7‑Sep‑2020 | Aix En Provence CH | Clay | R16 | 120 | 219 | (SE)Oscar Otte [GER] d. Mayer | 7-6(5) 6-3 | | 0.65 | 5.6% | 2.8% | 62.0% | 77.3% | 44.4% | 4/6 | 1:40 |
| 7‑Sep‑2020 | Aix En Provence CH | Clay | R32 | 120 | 97 | Mayer d. (4)Hugo Dellien [BOL] | 6-3 6-2 | | 2.35 | 11.6% | 0.0% | 62.8% | 85.2% | 68.8% | 3/4 | 2:59 |
| 31‑Aug‑2020 | US Open | Hard | R128 | 120 | 18 | (25)Milos Raonic [CAN] d. Mayer | 6-3 6-2 6-3 | | 0.45 | 6.0% | 8.4% | 54.2% | 62.2% | 47.4% | 4/9 | 1:49 |
| 6‑Mar‑2020 | Davis Cup QLS R1: ARG vs COL | Clay | RR | 118 | 148 | Daniel Elahi Galan [COL] d. Mayer | 6-1 6-4 | | 0.54 | 0.0% | 10.2% | 51.0% | 64.0% | 29.2% | 2/7 | 1:08 |
| 24‑Feb‑2020 | Santiago | Clay | R32 | 111 | 88 | (8)Thiago Monteiro [BRA] d. Mayer | 6-7(0) 6-3 6-4 | | 0.86 | 1.9% | 4.9% | 59.2% | 67.2% | 59.5% | 6/8 | 2:31 |
| 17‑Feb‑2020 | Rio De Janeiro | Clay | R32 | 109 | 52 | Lorenzo Sonego [ITA] d. Mayer | 6-1 5-7 6-4 | | 0.84 | 0.0% | 12.1% | 49.5% | 62.2% | 56.5% | 3/6 | 2:51 |
| 10‑Feb‑2020 | Buenos Aires | Clay | R32 | 107 | 42 | (7)Albert Ramos [ESP] d. (WC)Mayer | 4-6 6-3 7-5 | | 0.84 | 10.5% | 7.0% | 68.6% | 74.6% | 51.9% | 4/6 | 2:14 |
| 3‑Feb‑2020 | Cordoba | Clay | R32 | 103 | 87 | Jaume Munar [ESP] d. Mayer | 6-4 6-3 | | 0.40 | 4.5% | 9.1% | 54.5% | 80.6% | 33.3% | 4/7 | 1:20 |
| 20‑Jan‑2020 | Australian Open | Hard | R128 | 101 | 80 | Tommy Paul [USA] d. Mayer | 4-6 6-4 6-4 6-4 | | 0.69 | 4.8% | 4.0% | 60.5% | 69.3% | 44.9% | 5/11 | 2:39 |
| 13‑Jan‑2020 | Auckland | Hard | R32 | 100 | 76 | Marco Cecchinato [ITA] d. (LL)Mayer | 7-6(6) 6-7(18) 7-6(2) | | 0.95 | 8.9% | 3.0% | 59.3% | 68.8% | 65.5% | 9/11 | 3:07 |
| 13‑Jan‑2020 | Auckland | Hard | Q2 | 100 | 86 | (4)Thiago Monteiro [BRA] d. (5)Mayer | 7-6(3) 4-6 6-1 | | 0.70 | 6.0% | 4.8% | 58.3% | 79.6% | 37.1% | 1/4 | 2:03 |
| 13‑Jan‑2020 | Auckland | Hard | Q1 | 100 | 901 | (5)Mayer d. Rhett Purcell [GBR] | 7-5 4-6 6-1 | | 1.34 | 6.3% | 3.8% | 63.7% | 72.5% | 65.5% | 2/5 | 1:53 |
