Walter Johnson has the lowest ERA for the Washington Senators in a season, with an ERA of 1.14 in 1913.

Interpreted as:

twins single season era with a minimum of 0.5 IP per team game leaders

	NAME	ERA	SEASON	TM	G	W	L	W%	GS	SO	CG	SHO	SV	IP	H	ER	R	HR	BB	HBP	GF	IBB	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	ERA-	FIP	FIP-	H/9	PRAA
1	Walter Johnson W. Johnson	1.14	1913	WSH	48	36	7	.837	36	243	29	11	2	346.0	232	44	56	9	38	9	10		1,271	2	6.32	0.99	6.39	0.23	19.1	3.0	0.78	.229	1.46	39	1.90	63	6.03	42.3
2	Walter Johnson W. Johnson	1.27	1918	WSH	39	23	13	.639	29	162	29	8	3	326.0	241	46	71	2	70	8	10		1,261	8	4.47	1.93	2.31	0.06	12.8	5.6	0.95	.235	1.96	47	2.04	74	6.65	25.9
3	Walter Johnson W. Johnson	1.36	1910	WSH	45	25	17	.595	42	313	38	8	1	370.0	262	56	92	1	76	13	3		1,367	21	7.61	1.85	4.12	0.02	22.9	5.6	0.91	.271	2.24	56	1.39	56	6.37	45.2
4	Walter Johnson W. Johnson	1.39	1912	WSH	50	33	12	.733	37	303	34	7	2	369.0	259	57	89	2	76	16	13		1,413	11	7.39	1.85	3.99	0.05	21.4	5.4	0.91	.253	2.17	42	2.03	63	6.32	49.6
5	Walter Johnson W. Johnson	1.49	1919	WSH	39	20	14	.588	29	147	27	7	2	290.1	235	48	73	0	51	7	10		1,131	4	4.56	1.58	2.88	0.00	13.0	4.5	0.99	.254	2.26	48	2.07	67	7.28	32.6
6	Walter Johnson W. Johnson	1.55	1915	WSH	47	27	13	.675	39	203	35	7	4	336.2	258	58	83	1	56	19	8		1,280	7	5.43	1.50	3.63	0.03	15.9	4.4	0.93	.257	2.22	53	1.91	65	6.90	38.3
7	Walter Johnson W. Johnson	1.65	1908	WSH	36	14	14	.500	30	160	23	6	1	256.1	194	47	75	0	53	11	6		985	13	5.62	1.86	3.02	0.00	16.2	5.4	0.96	.255	2.63	72	1.60	75	6.81	15
8	Bill Burns B. Burns	1.70	1908	WSH	23	6	11	.353	19	55	11	2	0	164.0	135	31	58	3	18	4	1		612	1	3.02	0.99	3.06	0.16	9.0	2.9	0.93	.248	3.18	74	2.07	96	7.41	0.7
9	Walter Johnson W. Johnson	1.72	1914	WSH	51	28	18	.609	40	225	33	9	1	371.2	287	71	88	3	74	11	9		1,406	14	5.45	1.79	3.04	0.07	16.0	5.3	0.97	.260	2.13	63	2.02	71	6.95	33.6
10	Eddie Matteson E. Matteson	1.73	1918	WSH	14	5	3	.625	6	17	2	0	0	67.2	57	13	20	2	15	1	5		257	0	2.26	2.00	1.13	0.27	6.6	5.8	1.06	.248	2.66	64	2.82	102	7.58	-0.7
11	Dick Hyde D. Hyde	1.75	1958	WSH	53	10	3	.769	0	49	0	0	19	103.0	82	20	26	1	35	2	44	7	416	2	4.28	3.06	1.40	0.09	11.8	8.4	1.14	.246	2.27	45	2.73	70	7.17	13
12	Harry Harper H. Harper	1.77	1915	WSH	19	4	4	.500	10	54	5	2	2	86.1	66	17	26	1	40	1	6		338	5	5.63	4.17	1.35	0.10	16.0	11.8	1.23	.269	2.71	61	2.73	93	6.88	1.8
13	Walter Johnson W. Johnson	1.88	1907	WSH	14	5	9	.357	12	71	11	2	0	110.1	100	23	35	1	20	2	2		432	4	5.79	1.63	3.55	0.08	16.4	4.6	1.09	.293	2.85	76	1.61	70	8.16	8.4
14	J.C. Romero	1.89	2002	MIN	81	9	2	.818	0	76	0	0	1	81.0	62	17	17	3	36	4	15	4	332	9	8.44	4.00	2.11	0.33	22.9	10.8	1.21	.277	1.89	42	3.04	71	6.89	11.3
15	Walter Johnson W. Johnson	1.90	1911	WSH	40	25	13	.658	37	207	36	6	1	322.1	292	68	119	8	70	8	3		1,306	17	5.78	1.95	2.96	0.22	15.8	5.4	1.12	.280	3.32	57	2.53	79	8.15	23.7
16	Walter Johnson W. Johnson	1.90	1916	WSH	48	25	20	.556	38	228	36	3	1	369.2	290	78	105	0	82	9	10		1,410	9	5.55	2.00	2.78	0.00	16.2	5.8	1.01	.266	2.56	68	1.82	65	7.06	39.7
17	Cy Falkenberg C. Falkenberg	1.96	1908	WSH	17	6	2	.750	8	34	5	1	0	82.2	70	18	29	2	21	2	5		320	4	3.70	2.29	1.62	0.22	10.6	6.6	1.10	.261	3.16	86	2.43	113	7.62	-3.1
18	Doug Corbett D. Corbett	1.98	1980	MIN	73	8	6	.571	0	89	0	0	23	136.1	102	30	31	7	42	1	63	8	531	3	5.88	2.77	2.12	0.46	16.8	7.9	1.06	.242	2.05	48	3.05	76	6.73	14.8
19	Stan Williams S. Williams	1.99	1970	MIN	68	10	1	.909	0	76	0	0	15	113.1	85	25	34	8	32	5	36	6	455	2	6.04	2.54	2.38	0.64	16.7	7.0	1.03	.231	2.70	52	3.19	79	6.75	10.6
20	Bill Dailey B. Dailey	1.99	1963	MIN	66	6	3	.667	0	72	0	0	21	108.2	80	24	26	9	19	0	43	5	414	2	5.96	1.57	3.79	0.75	17.4	4.6	0.91	.226	2.15	54	2.76	74	6.63	11.6
21	Jim Kaat J. Kaat	2.06	1972	MIN	15	10	2	.833	15	64	5	0	0	113.1	94	26	36	6	20	0	0	2	443	2	5.08	1.59	3.20	0.48	14.4	4.5	1.01	.249	2.86	66	2.48	76	7.46	9.7
22	Ron Perranoski R. Perranoski	2.11	1969	MIN	75	9	10	.474	0	62	0	0	31	119.2	85	28	32	4	52	1	52	16	484	0	4.66	3.91	1.19	0.30	12.8	10.7	1.14	.222	2.41	57	3.23	84	6.39	8.1
23	Roger Wolff R. Wolff	2.12	1945	WSH	33	20	10	.667	29	108	21	4	2	250.0	200	59	68	7	53	1	4		1,000	1	3.89	1.91	2.04	0.25	10.8	5.3	1.01	.232	2.45	66	2.69	81	7.20	17.7
24	Dutch Leonard D. Leonard	2.13	1945	WSH	31	17	7	.708	29	96	12	4	1	216.0	208	51	72	5	35	2	1		885	2	4.00	1.46	2.74	0.21	10.8	4.0	1.13	.272	3.00	66	2.47	74	8.67	20.9
25	Joe Boehling J. Boehling	2.14	1913	WSH	38	17	7	.708	25	110	18	3	4	235.1	197	56	82	3	82	9	9		924	6	4.21	3.14	1.34	0.11	11.9	8.9	1.19	.269	3.14	73	2.95	98	7.53	1.3