Walter Johnson has the best career ERA for the Washington Senators, with an ERA of 2.17.

Interpreted as:

player with the best era with a minimum of 750 IP all-time twins

	NAME	ERA	IP	G	W	L	W%	GS	SO	CG	SHO	SV	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	2.17	5914.1	802	417	279	.599	666	3,509	531	110	34	4,913	1,424	1,902	97	1,363	205	127		23,405	154	5.34	2.07	2.57	0.15	15.0	5.8	1.06	.264	2.89	68	2.42	76	7.48	472.8
2	Doc Ayers D. Ayers	2.64	1122.1	227	52	61	.460	111	487	47	13	14	1,043	329	453	15	287	39	83		4,444	12	3.91	2.30	1.70	0.12	11.0	6.5	1.19	.284	3.63	96	2.52	90	8.36	35.9
3	Harry Harper H. Harper	2.75	1037.0	183	48	58	.453	141	526	51	11	5	877	317	429	12	488	36	26		4,254	51	4.57	4.24	1.08	0.10	12.4	11.5	1.32	.271	3.72	98	2.99	105	7.61	-19.3
4	Charlie Smith C. Smith	2.77	822.2	118	31	61	.337	91	379	59	7	1	810	253	365	8	223	17	24		3,360	26	4.15	2.44	1.70	0.09	11.3	6.6	1.26	.293	3.99	113	2.30	99	8.86	-0.1
5	Bert Gallia B. Gallia	2.83	855.0	169	44	42	.512	87	384	36	5	7	777	269	361	8	309	23	56		3,453	27	4.04	3.25	1.24	0.08	11.1	8.9	1.27	.282	3.80	102	2.75	97	8.18	8
6	Joe Boehling J. Boehling	2.86	805.1	135	53	39	.576	100	363	53	9	4	732	256	329	12	337	32	27		3,283	22	4.06	3.77	1.08	0.13	11.1	10.3	1.33	.284	3.68	100	3.11	107	8.18	-19.2
7	Tom Hughes T. Hughes	3.02	1776.0	285	84	124	.404	205	884	139	17	15	1,726	595	857	38	567	67	67		7,329	51	4.48	2.87	1.56	0.19	12.1	7.7	1.29	.292	4.34	111	2.79	105	8.75	-34.3
8	Bob Groom B. Groom	3.04	1353.1	195	72	89	.447	169	699	104	12	3	1,287	457	630	30	424	40	19		5,503	42	4.65	2.82	1.65	0.20	12.7	7.7	1.26	.292	4.19	106	2.84	101	8.56	-0.4
9	Jim Shaw J. Shaw	3.07	1600.1	287	84	98	.462	194	767	96	17	16	1,446	546	677	28	688	24	66		6,574	58	4.31	3.87	1.11	0.16	11.7	10.5	1.33	.280	3.81	102	3.04	101	8.13	-12.9
10	Jim Perry J. Perry	3.15	1883.1	376	128	90	.587	249	1,025	61	17	5	1,711	659	736	166	541	50	35	56	7,791	37	4.90	2.59	1.89	0.79	13.2	6.9	1.20	.257	3.52	89	3.50	96	8.18	35.4
11	Johan Santana J. Santana	3.22	1308.2	251	93	44	.679	175	1,381	6	4	1	1,068	468	500	144	364	27	23	2	5,281	55	9.50	2.50	3.79	0.99	26.2	6.9	1.09	.275	3.44	71	3.30	76	7.34	154.5
12	Dutch Leonard D. Leonard	3.27	1899.1	262	118	101	.539	251	657	130	23	2	1,951	690	852	84	403	30	6		7,956	55	3.11	1.91	1.63	0.40	8.3	5.1	1.24	.275	4.04	86	3.25	86	9.24	109.1
13	Bert Blyleven B. Blyleven	3.28	2566.2	348	149	138	.519	345	2,035	141	29	0	2,369	934	1,044	243	674	80	2	37	10,542	56	7.14	2.36	3.02	0.85	19.3	6.4	1.19	.283	3.66	84	3.14	81	8.31	202.7
14	Mickey Haefner M. Haefner	3.29	1291.2	215	73	77	.487	156	464	84	12	12	1,224	472	562	53	479	32	37		5,528	15	3.23	3.34	0.97	0.37	8.4	8.7	1.32	.260	3.92	94	3.50	100	8.53	-2.3
15	Jim Kaat J. Kaat	3.34	3014.1	484	190	159	.544	433	1,851	133	23	5	2,982	1,118	1,343	279	729	96	20	61	12,642	106	5.53	2.18	2.54	0.83	14.6	5.8	1.23	.279	4.01	91	3.33	88	8.90	148.3
16	Casey Patten C. Patten	3.34	2059.1	269	106	127	.455	237	757	206	17	4	2,146	765	1,074	40	556	74	28		8,606	28	3.31	2.43	1.36	0.17	8.8	6.5	1.31	.293	4.69	115	2.98	105	9.38	-26.9
17	Mudcat Grant M. Grant	3.35	780.2	129	50	35	.588	111	377	36	10	1	783	291	340	88	163	7	6	6	3,227	16	4.35	1.88	2.31	1.01	11.7	5.1	1.21	.268	3.92	94	3.70	100	9.03	0.8
18	Bob Porterfield B. Porterfield	3.38	1041.2	146	67	64	.511	138	366	78	19	0	1,020	391	437	62	343	10	7	5	4,361	7	3.16	2.96	1.07	0.54	8.4	7.9	1.31	.268	3.78	89	3.54	94	8.81	27.3
19	George Mogridge G. Mogridge	3.38	1016.2	145	68	55	.553	136	284	72	12	1	1,104	382	453	38	273	32	7		4,341	9	2.51	2.42	1.04	0.34	6.5	6.3	1.35	.287	4.01	85	3.86	98	9.77	6.7
20	Dave Goltz D. Goltz	3.48	1638.0	247	96	79	.549	215	887	80	11	3	1,654	634	729	119	493	24	15	19	6,887	54	4.87	2.71	1.80	0.65	12.9	7.2	1.31	.286	4.01	90	3.43	90	9.09	73.9
21	Dave Boswell D. Boswell	3.49	1036.1	187	67	54	.554	150	865	37	6	0	823	402	443	106	460	34	6	15	4,344	43	7.51	3.99	1.88	0.92	19.9	10.6	1.24	.249	3.85	100	3.60	99	7.15	4.7
22	Firpo Marberry F. Marberry	3.59	1654.0	470	117	71	.622	133	667	64	5	94	1,620	659	769	69	568	37	251		6,994	10	3.63	3.09	1.17	0.38	9.5	8.1	1.32	.274	4.18	85	3.93	94	8.81	41.7
23	Camilo Pascual C. Pascual	3.66	2465.0	432	145	141	.507	331	1,885	119	31	10	2,283	1,002	1,127	214	909	47	60	42	10,471	69	6.88	3.32	2.07	0.78	18.0	8.7	1.29	.279	4.11	95	3.27	84	8.34	176
24	Happy Townsend H. Townsend	3.68	901.1	117	22	69	.242	97	370	85	2	0	944	369	522	20	321	46	19		3,862	43	3.69	3.21	1.15	0.20	9.6	8.3	1.40	.298	5.21	127	3.25	114	9.43	-40.2
25	Alex Carrasquel A. Carrasquel	3.68	857.1	255	50	39	.562	64	251	30	4	16	879	351	420	41	343	6	125		3,738	13	2.63	3.60	0.73	0.43	6.7	9.2	1.43	.271	4.41	101	3.87	107	9.23	-27.2