diff --git a/src/NSwag.CodeGeneration.Tests/CodeGenerationTests.cs b/src/NSwag.CodeGeneration.Tests/CodeGenerationTests.cs
index e01227b81..b1f682aab 100644
--- a/src/NSwag.CodeGeneration.Tests/CodeGenerationTests.cs
+++ b/src/NSwag.CodeGeneration.Tests/CodeGenerationTests.cs
@@ -84,8 +84,8 @@ public void When_using_MultipleClientsFromFirstTagAndOperationName_then_ensure_t
         }
 
         [Theory(DisplayName = "Ensure expected operation name generation when using MultipleClientsFromFirstTagAndOperationName behavior")]
-        [InlineData("OperationId_SecondUnderscore_Test", "Test")]
-        [InlineData("OperationId_MultipleUnderscores_Client_Test", "Test")]
+        [InlineData("OperationId_SecondUnderscore_Test", "SecondUnderscore_Test")]
+        [InlineData("OperationId_MultipleUnderscores_Client_Test", "MultipleUnderscores_Client_Test")]
         [InlineData("OperationId_Test", "Test")]
         [InlineData("UnderscoreLast_", "UnderscoreLast_")]
         [InlineData("_UnderscoreFirst", "UnderscoreFirst")]
@@ -111,8 +111,8 @@ public void When_using_MultipleClientsFromFirstTagAndOperationName_then_ensure_t
         }
 
         [Theory(DisplayName = "Ensure expected client name generation with different operationIds when using the MultipleClientsFromOperationId behavior")]
-        [InlineData("OperationId_SecondUnderscore_Test", "SecondUnderscore")]
-        [InlineData("OperationId_MultipleUnderscores_Client_Test", "Client")]
+        [InlineData("OperationId_SecondUnderscore_Test", "OperationId")]
+        [InlineData("OperationId_MultipleUnderscores_Client_Test", "OperationId")]
         [InlineData("OperationId_Test", "OperationId")]
         [InlineData("UnderscoreLast_", "UnderscoreLast")]
         [InlineData("_UnderscoreFirst", "")]
@@ -139,5 +139,59 @@ public void When_using_MultipleClientsFromOperationId_then_ensure_that_underscor
             // Assert
             Assert.Equal(expectedClientName, clientName);
         }
+
+        [Theory(DisplayName = "Ensure expected operation name generation with different operationIds when using the MultipleClientsFromOperationId behavior")]
+        [InlineData("OperationId_SecondUnderscore_Test", "SecondUnderscore_Test")]
+        [InlineData("OperationId_MultipleUnderscores_Client_Test", "MultipleUnderscores_Client_Test")]
+        [InlineData("OperationId_Test", "Test")]
+        [InlineData("UnderscoreLast_", "UnderscoreLast_")]
+        [InlineData("_UnderscoreFirst", "UnderscoreFirst")]
+        [InlineData("NoUnderscore", "NoUnderscore")]
+        public void When_using_MultipleClientsFromOperationId_then_ensure_that_operationname_is_correct(string operationId, string expectedOperationName)
+        {
+            // Arrange
+            var operation = new OpenApiOperation
+            {
+                OperationId = operationId
+            };
+            var generator = new MultipleClientsFromOperationIdOperationNameGenerator();
+
+            var document = new OpenApiDocument();
+            var path = string.Empty;
+            var httpMethod = string.Empty;
+
+            // Act
+            string operationName = generator.GetOperationName(document, path, httpMethod, operation);
+
+            // Assert
+            Assert.Equal(expectedOperationName, operationName);
+        }
+
+        [Theory(DisplayName = "Ensure unique (client, operation) pairs when using MultipleClientsFromOperationId to avoid duplicate method names")]
+        [InlineData("Orders_items_get", "Products_items_get")]
+        [InlineData("Resource1_getSomething", "Resource2_getSomething")]
+        [InlineData("A_B_C", "D_B_C")]
+        public void When_using_MultipleClientsFromOperationId_then_unique_operationIds_produce_unique_client_operation_pairs(string operationId1, string operationId2)
+        {
+            // Arrange
+            var operation1 = new OpenApiOperation { OperationId = operationId1 };
+            var operation2 = new OpenApiOperation { OperationId = operationId2 };
+            var generator = new MultipleClientsFromOperationIdOperationNameGenerator();
+
+            var document = new OpenApiDocument();
+            var path = string.Empty;
+            var httpMethod = string.Empty;
+
+            // Act
+            string clientName1 = generator.GetClientName(document, path, httpMethod, operation1);
+            string operationName1 = generator.GetOperationName(document, path, httpMethod, operation1);
+            string clientName2 = generator.GetClientName(document, path, httpMethod, operation2);
+            string operationName2 = generator.GetOperationName(document, path, httpMethod, operation2);
+
+            // Assert: unique operation IDs must not produce the same (client, operation) pair
+            Assert.False(
+                clientName1 == clientName2 && operationName1 == operationName2,
+                $"OperationIds '{operationId1}' and '{operationId2}' produced duplicate (client='{clientName1}', operation='{operationName1}') pair");
+        }
     }
 }
diff --git a/src/NSwag.CodeGeneration/OperationNameGenerators/MultipleClientsFromOperationIdOperationNameGenerator.cs b/src/NSwag.CodeGeneration/OperationNameGenerators/MultipleClientsFromOperationIdOperationNameGenerator.cs
index b3d946e68..f74ab831e 100644
--- a/src/NSwag.CodeGeneration/OperationNameGenerators/MultipleClientsFromOperationIdOperationNameGenerator.cs
+++ b/src/NSwag.CodeGeneration/OperationNameGenerators/MultipleClientsFromOperationIdOperationNameGenerator.cs
@@ -81,42 +81,23 @@ public virtual string GetOperationName(OpenApiDocument document, string path, st
         private static ReadOnlySpan<char> GetClientName(OpenApiOperation operation)
         {
             ReadOnlySpan<char> operationIdSpan = operation.OperationId.AsSpan();
-            const char underscoreSeparator = '_';
-            int idxFirst = operationIdSpan.IndexOf(underscoreSeparator);
+            int idx = operationIdSpan.IndexOf('_');
 
-            // no underscore, fast path
-            if (idxFirst == -1)
+            // no underscore or underscore is the first character
+            if (idx <= 0)
             {
                 return [];
             }
 
-            int idxLast = operationIdSpan.LastIndexOf(underscoreSeparator);
-
-            // only one underscore
-            if (idxFirst == idxLast)
-            {
-                // underscore is the first character
-                if (idxFirst == 0)
-                {
-                    return [];
-                }
-
-                return operationIdSpan.Slice(0, idxFirst);
-            }
-
-            // backwards search for the second underscore
-            // e.g. OperationId_SecondUnderscore_Test => SecondUnderscore
-            operationIdSpan = operationIdSpan.Slice(0, idxLast);
-            int idxSecondLast = operationIdSpan.LastIndexOf(underscoreSeparator);
-
-            return operationIdSpan.Slice(idxSecondLast + 1);
+            return operationIdSpan.Slice(0, idx);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static ReadOnlySpan<char> GetOperationName(OpenApiOperation operation)
         {
             var span = operation.OperationId.AsSpan();
-            var idx = span.LastIndexOf('_');
+            var idx = span.IndexOf('_');
+            // No underscore, or underscore is the last character: return the full operation ID
             return idx != -1 && idx < span.Length - 1
                 ? span.Slice(idx + 1)
                 : span;